Add f2fs, by Jaegeuk Kim <jaegeuk.kim@samsung.com>

    f2fs: add document
    f2fs: add on-disk layout
    f2fs: add superblock and major in-memory structure
    f2fs: add super block operations
    f2fs: add checkpoint operations
    f2fs: add node operations
    f2fs: add segment operations
    f2fs: add file operations
    f2fs: add address space operations for data
    f2fs: add core inode operations
    f2fs: add inode operations for special inodes
    f2fs: add core directory operations
    f2fs: add xattr and acl functionalities
    f2fs: add garbage collection functions
    f2fs: add recovery routines for roll-forward
    f2fs: move proc files to debugfs
    f2fs: update Kconfig and Makefile
    f2fs: update the f2fs document
    f2fs: remove unneeded version.h header file from f2fs.h
    f2fs: fix endian conversion bugs reported by sparse
    f2fs: adjust kernel coding style
    f2fs: resolve build failures
    f2fs: fix the compiler warning for uninitialized use of variable
    f2fs: show error in case of invalid mount arguments
    f2fs: remove unneeded memset from init_once
    f2fs: check read only condition before beginning write out
    f2fs: remove unneeded initialization
    f2fs: move error condition for mkdir at proper place
    f2fs: remove unused variable
    f2fs: fix a typo in f2fs documentation
    f2fs: rewrite f2fs_bio_alloc to make it simpler
    f2fs: make use of GFP_F2FS_ZERO for setting gfp_mask
    f2fs: remove redundant call to f2fs_put_page in delete entry
    f2fs: introduce accessor to retrieve number of dentry slots
    f2fs: cleanup the f2fs_bio_alloc routine
    f2fs: fix tracking parent inode number
    update defconfig

Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Chul Lee <chur.lee@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Huajun Li <huajun.li.lee@gmail.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Pankaj Kumar <pankaj.km@samsung.com>
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>