sim: nltvals: localize TARGET_<open> defines

Code should not be using these directly, instead they should be
resolving these dynamically via the open_map.  Rework the common
callback code that was using the defines to use symbolic names
instead, and localize some of the defines in the ARM code (since
it's a bit unclear how many different APIs it supports currently),
then remove the defines out of the header so no new code can rely on
them.