drm/amdgpu/vcn: Add MMSCH v4_0_3 support for sriov

The structures are the same as v4_0 except for the
init header

Signed-off-by: Samir Dhume <samir.dhume@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>