radv: fix various CMASK regressions on GFX9

This fixes a bunch of MSAA related CTS regressions. This restores
previous behaviour on GFX9 but it should be fixed properly.

Cc: 21.1 mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <!10374>
34 jobs for !10374 with radv_fix_cmask_regressions_gfx9 in 11 minutes and 19 seconds (queued for 3 seconds)
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