drm/amdgpu: add new uvd enc ring methods

Add new UVD encode ring methods get/set/emit/flush/sync to support uvd6.3 HEVC encoding

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