drm/msm/gpu: Also snapshot GMU HFI buffer

This also includes a history of start index of the last 8 messages on
each queue, since parsing backwards to decode recently sent HFI messages
is hard(ish).

Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20211124214151.1427022-9-robdclark@gmail.com
Signed-off-by: Rob Clark <robdclark@chromium.org>