a) When the vm_node is freed in ttm_bo.c b) When we transfer a buffer object in ttm_bo_util.c Reported by Jerome Glisse.
Fix destruction and initalization of "ghost" buffer objects that are created on pipelined buffer moves. Reported and suggestions by Jerome Glisse. Signed-off-by: Thomas Hellstrom <thellstrom-at-vmware-dot-com>