High PC speaker frequencies treated as constant level.

Improved timing for port 0x61 writes.

src/keyboard_xt.c

@@ -76,6 +76,9 @@ void keyboard_xt_write(uint16_t port, uint8_t val, void *priv)
                 keyboard_xt.pb = val;
                 ppi.pb = val;
 
+                timer_process();
+                timer_update_outstanding();
+        
                 speaker_gated = val & 1;
                 speaker_enable = val & 2;
                 if (speaker_enable)