If a per VM BO ends up in a allowed domain it never moves back into the
prefered domain.

v2: move the extra handling into amdgpu_vm_bo_update when we exit the
    state machine. Make memory type handling generic.
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NChunming Zhou <david1.zhou@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>