drm/nouveau: wait on fence after bo move if validating for another channel

Not an ideal solution, but it'll do for the moment for correctness.  We
need to come up with a nicer way to manage inter-channel sync, the hw
is unfortunately a little lacking in this area.

Should fix some resume corruption, as well as corruption that may be seen
while under memory pressure.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -469,6 +469,8 @@ nouveau_bo_move_accel_cleanup(struct nouveau_channel *chan,
 
 	ret = ttm_bo_move_accel_cleanup(&nvbo->bo, fence, NULL,
 					evict, no_wait, new_mem);
+	if (nvbo->channel && nvbo->channel != chan)
+		ret = nouveau_fence_wait(fence, NULL, false, false);
 	nouveau_fence_unref((void *)&fence);
 	return ret;
 }