This reverts commit 930e2607 ("f2fs: remove obsolete whint_mode"), as we
decide to pass write hints to the disk.

Cc: Hyunchul Lee <cheol.lee@lge.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>