panfrost: Disable AFBC on v7 due to multiple hard to fix bugs

Cc @bbrezillon -- I really don't want to land the last commit here but I've been pretty stumped with the debug. In theory the reverse issue order flag should fix the AFBC preload, but it doesn't... and this -might- be an issue on midgard/v6 too? Worth investigation.

As for the G31 without AFBC issue reported on IRC, I have a kernel patch for this but even in the best case it won't hit a stable tree any time soon (and I doubt we can argue a UABI change qualifies as a bugfix for backport.)