gallium: Allow copy_region blits with matching formats.

gallium: Allow copy_region blits with matching formats.

If the blit formats match and the resource formats match, then that's a
memcpy whether or not the blit's view of the resource matches the
resource's format.

Improves perf of portal-2-v2's last frame on zink+anv by 1.33212% +/-
0.302829% (n=5), where there's a blit that is viewing the RGBA8_UNORM
src/dst resources as RGBA8_SRGB.

Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20594>