panfrost: Disable AFBC on v7

Broken in several ways. Hide it until we can get this sorted, and have a
test plan to keep it sorted.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Cc: mesa-stable
49 jobs for !11120 with disable-afbc-sigh in 32 minutes and 29 seconds (queued for 5 seconds)
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