drm/msm/a6xx: A640/A650 GMU firmware path

Newer GPUs have different GMU firmware path.

v3: updated a6xx_gmu_fw_load based on feedback, including gmu_write_bulk,
and removed extra whitespace change

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>