drm/amd/amdgpu: Enable arcturus devices to access the method kgd_gfx_v9_get_cu_occupancy that is already defined

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

[How]
Remove the keyword static for the method kgd_gfx_v9_get_cu_occupancy
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Ramesh Errabolu <Ramesh.Errabolu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>