fsck.ubifs: Add file organization realization

fsck.ubifs: Add file organization realization

In order to check the consistency of each file and the reachability of
the whole dentry tree, fsck orginizes all nodes into files. And the
final recovered file(xattr is treated as a file) is organized as:
   (rbtree, inum indexed)
        /    \
     file1   file2
     /    \
  file3  file4

file {
        inode node // each file has 1 inode node
        dentry (sub rb_tree, sqnum indexed) // '/' has no dentries,
                                            // otherwise at least 1
                                            // dentry is required.
        trun node // the newest one truncation node
        data (sub rb_tree, block number indexed) // Each file may have 0
                                                 // or many data nodes
	xattrs (sub rb_tree, inum indexed) // Each file may have 0 or
                                           // many xattr files
}

Each file from file rb_tree is constructed by scanning nodes(eg. inode,
dentry, etc.) from the TNC or the UBI volume. File's xattrs will be
initialized in subsequent steps.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>