This patch integrates the below patch into f2fs.

"ext4 crypto: get rid of ci_mode from struct ext4_crypt_info

The ci_mode field was superfluous, and getting rid of it gets rid of
an unused hole in the structure."
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

This patch copies from encrypt_key.c in ext4, and modifies for f2fs.

Use GFP_NOFS, since _f2fs_get_encryption_info is called under f2fs_lock_op.
Signed-off-by: NMichael Halcrow <mhalcrow@google.com>
Signed-off-by: NIldar Muslukhov <muslukhovi@gmail.com>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

This definitions will be used by inode and superblock for encyption.
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>