block: move bdi/address_space unplug functions to backing-dev.h

There's nothing block related about them, the backing device
is used by things like NFS etc as well. This gets rid of the
need to protect such calls by CONFIG_BLOCK.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index b449e73..fcbc26a 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -331,4 +331,17 @@
 	return 0;
 }
 
+static inline void blk_run_backing_dev(struct backing_dev_info *bdi,
+				       struct page *page)
+{
+	if (bdi && bdi->unplug_io_fn)
+		bdi->unplug_io_fn(bdi, page);
+}
+
+static inline void blk_run_address_space(struct address_space *mapping)
+{
+	if (mapping)
+		blk_run_backing_dev(mapping->backing_dev_info, NULL);
+}
+
 #endif		/* _LINUX_BACKING_DEV_H */