fsck.f2fs: introduce -p option to check meta

fsck.f2fs: introduce -p option to check meta

This patch introduces a new option '-p' to do more checks on NAT/SIT areas.
'-p' has 2 levels: level 1 has the same sematics as '-a'; level 2 checks
NAT/SIT counters to see if they matches the status in SB and CP.

A new function, fsck_chk_meta, is called by '-p 1' to implement these
comparsion. If errors are detected, fix_on is set, which means fsck will
do a 'fsck -f' immediately.

Signed-off-by: Sheng Yong <shengyong1@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>