This catches evictions of shadow page tables from the GART. Since shadow
page tables are always stored in system memory, amdgpu_bo_move is never
called for them.

This fixes a crash during command submission that occurs when only a shadow
page table and no other BOs were evicted since the last submission.

Fixes: 1baa439f ("drm/amdgpu: allocate shadow for pd/pt bo V2")
Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>