drm/amdgpu: use paging queue for VM page table updates

Only for testing, not sure if we should keep it like this.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>