mtd-utils: Extract list implementation to common lib and add list_sort support

mtd-utils: Extract list implementation to common lib and add list_sort support

Current list implementation code is put under jffs utils, extract it into
common lib, and add more list operations(eg. list_move, list_splice, etc.).
Besides, add list sorting support in new source file lib/list_sort.c.

This is a preparation for replacing implementation of UBIFS utils with
linux kernel libs.

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