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/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index cc673dd..a5226df 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -439,7 +439,7 @@
 {
 	int err;
 
-	err = simple_pin_fs("rpc_pipefs", &rpc_mount, &rpc_mount_count);
+	err = simple_pin_fs(&rpc_pipe_fs_type, &rpc_mount, &rpc_mount_count);
 	if (err != 0)
 		return ERR_PTR(err);
 	return rpc_mount;