drm/amdgpu: add high priority compute support for gfx9

We follow the same approach as gfx8. The only changes are register
access macros.

Tested on vega10. The execution latency results fall within the expected
ranges from the polaris10 data.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>