f2fs: support project quota

This patch adds to support plain project quota.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/filesystems/f2fs.txt

@@ -164,6 +164,7 @@ io_bits=%u             Set the bit size of write IO requests. It should be set
                        with "mode=lfs".
 usrquota               Enable plain user disk quota accounting.
 grpquota               Enable plain group disk quota accounting.
+prjquota               Enable plain project quota accounting.
 
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