i965: Export format comparison for blitting between miptrees

i965: Export format comparison for blitting between miptrees

Since the introduction of

commit 536003c11e4cb1172c540932ce3cce06f03bf44e
Author: Boyan Ding <boyan.j.ding@gmail.com>
Date:   Wed Mar 25 19:36:54 2015 +0800

    i965: Add XRGB8888 format to intel_screen_make_configs

winsys buffers no longer have an alpha channel. This causes
_mesa_format_matches_format_and_type() to reject previously working BGRA
uploads from using the BLT fast path. Instead of using the generic
routine for matching formats exactly, export the slightly more relaxed
check from intel_miptree_blit() which importantly allows the blitter
routine to apply a small number of format conversions.

References: https://bugs.freedesktop.org/show_bug.cgi?id=90839
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Alexander Monakov <amonakov@gmail.com>
Cc: Kristian Høgsberg <krh@bitplanet.net>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: mesa-stable@lists.freedesktop.org