f2fs: support 3.0

Initial backporting done by nowcomputing,
(https://github.com/nowcomputing/f2fs-backports.git)

Additional patches required by upstream jaegeuk/f2fs.git/linux-3.4 done by arter97.

Signed-off-by: Park Ju Hyung <qkrwngud825@gmail.com>

Conflicts:

	fs/f2fs/namei.c