f2fs: support plain user/group quota

This patch adds to support plain user/group quota.

Change Note by Jaegeuk Kim.

- Use f2fs page cache for quota files in order to consider garbage collection.
  so, quota files are not tolerable for sudden power-cuts, so user needs to do
  quotacheck.

- setattr() calls dquot_transfer which will transfer inode->i_blocks.
  We can't reclaim that during f2fs_evict_inode(). So, we need to count
  node blocks as well in order to match i_blocks with dquot's space.

  Note that, Chao wrote a patch to count inode->i_blocks without inode block.
  (f2fs: don't count inode block in in-memory inode.i_blocks)

- in f2fs_remount, we need to make RW in prior to dquot_resume.

- handle fault_injection case during f2fs_quota_off_umount

- TODO: Project quota

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index 8b04a63..273ccb2 100644
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -162,6 +162,8 @@
                        writes towards main area.
 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.
 
 ================================================================================
 DEBUGFS ENTRIES