drm/amdgpu: add optional ring to amdgpu_sync_is_idle

Check if the sync object is idle depending on the ring a submission works with.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>