gallium/util: Add helpers to determine if z/s is written

For drivers that must control various 'early-z'-like state, it is easy
enough to get this wrong.  So add helpers so we don't have to duplicate
the logic in each driver.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8598>
1 file changed