drm/amdgpu: set mmhub bitmask for multiple AIDs

Like GFXHUB, set MMHUB0 bitmask for each AID.

Signed-off-by: Le Ma <le.ma@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>