drm/amdgpu: Derive active clusters from SDMA

SDMA instances per active cluster and SDMA instance mask are used
to find the number of active clusters.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>