libfs: support RENAME_NOREPLACE in simple_rename()

This is trivial to do:

 - add flags argument to simple_rename()
 - check if flags doesn't have any other than RENAME_NOREPLACE
 - assign simple_rename() to .rename2 instead of .rename

Filesystems converted:

hugetlbfs, ramfs, bpf.

Debugfs uses simple_rename() to implement debugfs_rename(), which is for
debugfs instances to rename files internally, not for userspace filesystem
access.  For this case pass zero flags to simple_rename().

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Alexei Starovoitov <ast@kernel.org>
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 72361ba..5ac27c9 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -748,7 +748,7 @@
 	old_name = fsnotify_oldname_init(old_dentry->d_name.name);
 
 	error = simple_rename(d_inode(old_dir), old_dentry, d_inode(new_dir),
-		dentry);
+			      dentry, 0);
 	if (error) {
 		fsnotify_oldname_free(old_name);
 		goto exit;