drm/amdgpu: rework page directory filling v2

Keep track off relocated PDs/PTs instead of walking and checking all PDs.

v2: fix root PD handling

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com> (v1)
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>