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.

sim/m32r/sim-main.h

@@ -15,9 +15,6 @@ typedef struct _sim_cpu SIM_CPU;
 #include "m32r-opc.h"
 #include "arch.h"
 
-/* These must be defined before sim-base.h.  */
-typedef USI sim_cia;
-
 #define SIM_ENGINE_HALT_HOOK(sd, cpu, cia) \
 do { \
   if (cpu) /* null if ctrl-c */ \