VFS: Unexport do_kern_mount() and clean up simple_pin_fs()

Replace all module uses with the new vfs_kern_mount() interface, and fix up
simple_pin_fs().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/configfs/mount.c b/fs/configfs/mount.c
index f920d30..be5d86a 100644
--- a/fs/configfs/mount.c
+++ b/fs/configfs/mount.c
@@ -118,7 +118,7 @@
 
 int configfs_pin_fs(void)
 {
-	return simple_pin_fs("configfs", &configfs_mount,
+	return simple_pin_fs(&configfs_fs_type, &configfs_mount,
 			     &configfs_mnt_count);
 }