drm/amdgpu: activate paging queue on SDMA v4

Implement all the necessary stuff to get those extra rings working.

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>