i965: Drop the maximum 3D texture size to 512 on Sandy Bridge

i965: Drop the maximum 3D texture size to 512 on Sandy Bridge

The RenderTargetViewExtent field of RENDER_SURFACE_STATE is supposed to be
set to the depth of a 3-D texture when rendering.  Unfortunatley, that
field is only 9 bits on Sandy Bridge and prior so we can't actually bind
a 3-D texturing for rendering if it has depth > 512.  On Ivy Bridge, this
field was bumpped to 11 bits so we can go all the way up to 2048.  On Iron
Lake and prior, we don't support layered rendering and we use OffsetX/Y
hacks to render to particular layers so 2048 is ok there too.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Cc: "11.1 11.2 12.0" <mesa-stable@lists.freedesktop.org>