intel: Refactor creation of hiz and mcs miptrees

intel: Refactor creation of hiz and mcs miptrees

Move the logic for creating the ancillary hiz and mcs miptress for winsys
and non-texture renderbuffers from intel_alloc_renderbuffer_storage to
intel_miptree_create_for_renderbuffer. Let's try to isolate complex
miptree logic to intel_mipmap_tree.c.

Without this refactor, code duplication would be required along the
intel_process_dri2_buffer codepath in order to create the mcs miptree.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>