nilfs2: add sufile function that can modify multiple segment usages

This is a preparation for the later cleanup patch ("nilfs2: remove
list of freeing segments").

This adds nilfs_sufile_updatev() to sufile, which can modify multiple
segment usages at a time.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

diff --cc fs/nilfs2/sufile.c
Simple merge

diff --cc fs/nilfs2/sufile.h
Simple merge