util: List implementation

util: List implementation

We need something more than wl_list when an item should be contained in
multiple lists. pepper_list_t can do this while it can be used in the same way
with wl_list. Don't use container_of for a node which is internally allocated.

Change-Id: I59aa1536205a6e8b5cf10136cfef19b8c90b1b4b