drm/radeon: add Mullins VCE support

VCE 2.0 just like the other CIK parts.

Signed-off-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>