util: added TLIST_*() macros

util: added TLIST_*() macros

The TLIST_*() macros are like the DLIST_*() macros, but take both a
head and tail pointer for the list. This means that adding an element
to the end of the list is efficient (it doesn't need to walk the
list).

We should move all uses of the DLIST_*() macros which use
DLIST_ADD_END() to use the TLIST_*() macros instead.