drm/amdgpu: init vmhubs bitmask for GC 9.4.3

Each XCD owns one GFXHUB.

v2: switch to the new VMHUB layout

Signed-off-by: Le Ma <le.ma@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>