drm/amd/amdgpu: Define and implement a function that collects number of

waves that are in flight.

[Why]
Allow user to know how many compute units (CU) 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: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>