drm/amdgpu: wait for VM to become idle during flush

Make sure that not only the entities are flush, but that
we also wait for the HW to finish all processing.

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