ceph: allow idmapped mounts

Now that we converted cephfs internally to account for idmapped mounts
allow the creation of idmapped mounts on by setting the FS_ALLOW_IDMAP
flag.

Cc: Jeff Layton <jlayton@kernel.org>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: ceph-devel@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index bab6123..eda4a26 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -1242,7 +1242,7 @@
 	.name		= "ceph",
 	.init_fs_context = ceph_init_fs_context,
 	.kill_sb	= ceph_kill_sb,
-	.fs_flags	= FS_RENAME_DOES_D_MOVE,
+	.fs_flags	= FS_RENAME_DOES_D_MOVE | FS_ALLOW_IDMAP,
 };
 MODULE_ALIAS_FS("ceph");