sim: example-synacor: move arch-specific settings to internal header

There's no need for these settings to be in sim-main.h which is shared
with common/ sim code, so move it all out to a new header which only
this port will include.

sim/example-synacor/sim-main.c

@@ -26,6 +26,8 @@
 
 #include "sim-main.h"
 #include "sim-signal.h"
+
+#include "example-synacor-sim.h"
 
 /* Get the register number from the number.  */
 static uint16_t