fsck.ubifs: Move common functions and data structures into check_space.c

fsck.ubifs: Move common functions and data structures into check_space.c

This is a preparation for adding LPT checking support. Move some data
structures and functions into check_space.c, also factor out some common
functions in libubifs:
 1. Move 'lpts' from rebuild module, make it resuable for non-rebuild_fs
    modes.
 2. Move function 'get_free_leb' from rebuild_fs.c, it could be reused in
    building LPT.
 3. Move function 'build_lpt' from rebuild_fs.c, it could be reused in
    building LPT.
 4. Factor out lpt nodes freeing into a new function ubifs_free_lpt_nodes.
 5. Factor out nnode dirty marking implementations into a new function
    ubifs_make_nnode_dirty.
 5. Export the function of nnode number calculation, calc_nnode_num is
    renamed as ubifs_calc_nnode_num.
 6. Export the function of making pnode dirty, do_make_pnode_dirty is
    renamed as ubifs_make_pnode_dirty.
 7. Rename next_pnode_to_dirty to ubifs_find_next_pnode and export it.
 8. Export free_buds and expend its parameters.

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