f2fs: add help function META_MAPPING

Introduce help function META_MAPPING() to get the cache meta blocks'
address space.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

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

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

diff --cc fs/f2fs/f2fs.h
Simple merge

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

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