btrfs: Add noflushoncommit mount option.

Add noflushoncommit mount option to disable flush on commit with
remount option.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt
index 13a7cac..303b49c 100644
--- a/Documentation/filesystems/btrfs.txt
+++ b/Documentation/filesystems/btrfs.txt
@@ -117,6 +117,7 @@
 	  "bug" - BUG() on a fatal error.  This is the default.
 	  "panic" - panic() on a fatal error.
 
+  noflushoncommit(*)
   flushoncommit
 	The 'flushoncommit' mount option forces any data dirtied by a write in a
 	prior transaction to commit as part of the current commit.  This makes