f2fs: support swap file w/ DIO

mainline inclusion
from mainline-v5.3-rc1
commit 4969c06a
category: bugfix
bugzilla: 13690
CVE: CVE-2019-19815

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Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Conflicts:
  fs/f2fs/f2fs.h
  fs/f2fs/data.c
[yyl: adjust context]

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Wei Fang <fangwei1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>