PIT: add alternative faster PIT

This is enabled by default on 486+ CPUs and can be forced disabled/enabled with pit_mode=0/1

src/machine/m_xt.c

@@ -24,7 +24,7 @@ machine_xt_common_init(const machine_t *model)
 {
     machine_common_init(model);
 
-    pit_ctr_set_out_func(&pit->counters[1], pit_refresh_timer_xt);
+    pit_devs[0].set_out_func(pit_devs[0].data, 1, pit_refresh_timer_xt);
 
     if (fdc_type == FDC_INTERNAL)
 	    device_add(&fdc_xt_device);