f2fs: add compat_ioctl to provide backward compatability

introduce compat_ioctl to regular files, but doesn't add this
functionality to f2fs_dir_operations.

While running a 32-bit busybox, I met an error like this:
(A is a directory)

chattr: reading flags on A: Inappropriate ioctl for device

This patch copies compat_ioctl from f2fs_file_operations and
fix this problem.

Signed-off-by: hujianyang <hujianyang@huawei.com>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>