drm/amd/amdgpu: Prepare implementation to support reporting of CU usage

[Why]
Allow user to know number of compute units (CU) that are in use at any
given moment.

[How]
Read registers of SQ that give number of waves that are in flight
of various queues. Use this information to determine number of CU's
in use.

Signed-off-by: Ramesh Errabolu <Ramesh.Errabolu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>