sim: unify sim_cia definition

sim: unify sim_cia definition

Almost every target defines sim_cia the same way -- either using the
address_word type directly, or a type of equivalent size.  The only
odd one out is sh64 (who has 32bit address_word and 64bit cia), and
even that case doesn't seem to make sense.  We'll put off clean up
though of sh64 and at least set up a sensible default for everyone.