drm/amdgpu: move mmhub ras_func init to ip specific file

mmhub ras is always owned by gpu driver. ras_funcs
initialization shall be done at ip level, instead of
putting it in common gmc interface file

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