Like ttm_bo_validate(), ttm_bo_init() might need to move BO and
the number of bytes moved by TTM should be reported. This can help
the throttle buffer migration mechanism to make a better decision.

v2: fix computation
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NSamuel Pitoiset <samuel.pitoiset@gmail.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>