panfrost: Implement AFBC

Replaces !6010 (closed)

On supported GPUs (Mali T760+, and currently only Midgard), let's use AFBC everywhere we can, including for textures. A nice performance boost on texture-heavy workloads that do not use (ASTC/ETC) compressed textures.

WIP because it can cause some hard-to-debug breakage I need to sort out (memory faults in certain cases sharing AFBC buffers across processes.) Logic error, fixed in latest change set.

SCANOUT operation is also kinda busted on rk3399 which needs investigation (partly a bug in the RK3399 kernel driver that's incorrectly missing the YTR flag, partly more memory faults.)