i965: Faking the ETC2 compression on Gen < 8 GPUs using two miptrees.

i965: Faking the ETC2 compression on Gen < 8 GPUs using two miptrees.

GPUs Gen < 8 cannot sample ETC2 formats. So far, they converted the
compressed EAC/ETC2 images to non-compressed RGBA images. When
GetCompressed* functions were called, the pixels were returned in this
RGBA format and not the compressed format that was expected.

Trying to fix this problem, we use a secondary shadow miptree to store the
decompressed data for the rendering and the main miptree to store the
compressed for the Get functions to work. Each time that the main miptree
is written with compressed data, we decompress them to RGB and update the
shadow. Then we use the shadow for rendering.

v2:
   - Fixes in the commit message (Nanley Chery)
   - Reversed the changes in brw_get_texture_swizzle and swapped the b, g
   values at the time that we decompress the data in the function:
   intel_miptree_update_etc_shadow of intel_mipmap_tree.c (Nanley Chery)
   - Simplified the format checks in the miptree_create function of the
   intel_mipmap_tree.c and reserved the call of the
   intel_lower_compressed_format for the case that we are faking the ETC
   support (Nanley Chery)
   - Removed the check for the auxiliary usage for the shadow miptree at
   creation (miptree_create of intel_mipmap_tree.c) as we won't use
   auxiliary buffers with these types of trees (Nanley Chery)
   - Set the etc_format of the non-ETC miptrees to MESA_FORMAT_NONE and
   removed the unecessary checks (Nanley Chery)
   - Fixed an unrelated indentation change (Nanley Chery)
   - Modified the function intel_miptree_finish_write to set the
   mt->shadow_needs_update to true to catch all the cases when we need to
   update the miptree (Nanley Chery)
   - In order to update the shadow miptree during the unmap of the
   main and always map the main (Nanley Chery) the following change was
   necessary: Splitted the previous update function that was updating all
   the mipmap levels and use two functions instead: one that updates one
   level and one that updates all of them. Used the first during unmap
   and the second before the rendering.
   - Removed the BRW_MAP_ETC_BIT flag and the mechanism to decide which
   miptree should be mapped each time and reversed all the changes in the
   higher level texture functions that upload data to textures as they
   aren't needed anymore.
   - Replaced the boolean needs_fake_etc with an inline function that
   checks when we need to fake the ETC compression (Nanley Chery)
   - Removed the initialization of the strides in the update function as
   the values will be overwritten by the intel_miptree_map call (Nanley
   Chery)
   - Used minify instead of division in the new update function
   intel_miptree_update_etc_shadow_levels in intel_mipmap_tree.c (Nanley
   Chery)
   - Removed the depth from the calculation of the number of slices in
   the new update function (intel_miptree_update_etc_shadow_levels of
   intel_mipmap_tree.c) as we don't need to support 3D ETC images.
   (Nanley Chery)

v3:
  - Renamed the rgba_fmt in function miptree_create
  (intel_mipmap_tree.c) to decomp_format as the format is not always in
  rgba order. (Nanley Chery)
  - Documented the new usage for the shadow miptree in the comment above
  the field in the intel_miptree struct in intel_mipmap_tree.h (Nanley
  Chery)
  - Removed the redundant flags from the mapping of the miptrees in
  intel_miptree_update_etc_shadow of intel_mipmap_tree.c (Nanley Chery)
  - Fixed the switch from surface's logical level to physical level in
  the intel_miptree_update_etc_shadow_levels of intel_mipmap_tree.c
  (Nanley Chery)
  - Excluded the Baytrail GPUs from the check for the ETC emulation as
  they support the ETC formats natively. (Nanley Chery)
  - Simplified the check if the format is BGRA in
  intel_miptree_update_etc_shadow of intel_mipmap_tree.c (Nanley Chery)

v4:
  - Removed the functions intel_miptree_(map|unmap)_etc and the check if
   we need to call them as with the new changes, they became unreachable.
   (Nanley Chery)
  - We'd rather calculate the level width and height using the shadow
  miptree instead of the main in intel_miptree_update_etc_shadow_levels of
  intel_mipmap_tree.c (Nanley Chery)
  - Fixed the format in the mt_surface_usage, set at the miptree creation,
   in miptree_create of intel_mipmap_tree.c (Nanley Chery)

v5:
  - Fixed the levels calculations in intel_mipmap_tree.c (Nanley Chery)
  - Update the flag shadow_needs_update outside the function
  intel_miptree_update_etc_shadow (Nanley Chery)
  - Fixed indentation error (Nanley Chery)

v6:
  - Fixed typo in commit message (Nanley Chery)
  - Simplified the assignment of the mt_fmt in the miptree_create of the
  intel_mipmap_tree.c (Nanley Chery)
  - Combined declarations and assignments where it was possible in the
  intel_miptree_update_etc_shadow and
  intel_miptree_update_etc_shadow_levels of the intel_mipmap_tree.c
  (Nanley Chery)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81843
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104272
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>