nilfs2: separate constructor of metadata files

This will displace nilfs_mdt_new() constructor with individual
metadata file constructors like nilfs_dat_new(), new_sufile_new(),
nilfs_cpfile_new(), and nilfs_ifile_new().

This makes it possible for each metadata file to have own
intialization code.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/sufile.h b/fs/nilfs2/sufile.h
index 0e99e5c..50d3191 100644
--- a/fs/nilfs2/sufile.h
+++ b/fs/nilfs2/sufile.h
@@ -62,6 +62,8 @@
 void nilfs_sufile_do_set_error(struct inode *, __u64, struct buffer_head *,
 			       struct buffer_head *);
 
+struct inode *nilfs_sufile_new(struct the_nilfs *nilfs, size_t susize);
+
 /**
  * nilfs_sufile_scrap - make a segment garbage
  * @sufile: inode of segment usage file