panfrost: Add missing alpha-first special formats

Not sure if these come up with OpenGL in practice.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <!7352>
42 jobs for !7352 with z28 in 8 minutes and 55 seconds (queued for 6 seconds)
merge request