drm/msm/a6xx: use AOP-initialized PDC for a650

SM8250 AOP firmware already sets up PDC registers for us, and it only needs
to be enabled. This path will be used for other newer GPUs.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Link: https://lore.kernel.org/r/20210608172808.11803-3-jonathan@marek.ca


Signed-off-by: Rob Clark <robdclark@chromium.org>