drm/radeon: enable UVD interrupts on CIK

The same as on evergreen.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reported-by: FrankR Huang <FrankR.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org