Starting with Stoney we support running UVD in VM mode as well.

v2: rebased, only enable on Polaris for now.
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>