PDP11, VAX: Support multiplexer input speeds greater than 9600bps for console, DZ, VH, DL and DC devices

Each of the speeds greater than 9600bps deliver a character in less than
1ms.  Computing inter-character delays in microseconds therefore can't
be precise enough to be well behaved.  Measuring the inter-character
delays in instructions (scalled by the calibrated clock) gets us the needed
precision.

sim_timer.c

@@ -1558,6 +1558,8 @@ pthread_mutex_unlock (&sim_timer_lock);
 pthread_cond_signal (&sim_timer_wake);                  /* wake the timer thread to deal with it */
 return SCPE_OK;
 #else
+sim_debug (DBG_TIM, &sim_timer_dev, "sim_timer_activate_after() - queue addition %s at %d (%d usecs)\n", 
+           sim_uname(uptr), inst_delay, usec_delay);
 return _sim_activate (uptr, inst_delay);                /* queue it now */
 #endif
 }