drm/amdgpu: add mmhub 9.4.1 header files for Acrturus

mmhub is the GPU memory hub used by SDMA and VCN.

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