f2fs: add unlikely() macro for compiler more aggressively

This patch adds unlikely() macro into the most of codes.
The basic rule is to add that when:
- checking unusual errors,
- checking page mappings,
- and the other unlikely conditions.

Change log from v1:
 - Don't add unlikely for the NULL test and error test: advised by Andi Kleen.

Cc: Chao Yu <chao2.yu@samsung.com>
Cc: Andi Kleen <andi@firstfloor.org>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

diff --cc fs/f2fs/checkpoint.c
Simple merge

diff --cc fs/f2fs/data.c
Simple merge

diff --cc fs/f2fs/file.c
Simple merge

diff --cc fs/f2fs/gc.c
Simple merge

diff --cc fs/f2fs/node.c
Simple merge

diff --cc fs/f2fs/recovery.c
Simple merge

diff --cc fs/f2fs/super.c
Simple merge

diff --cc fs/f2fs/xattr.c
Simple merge