adds soft pwm for non-timed ports

quantum/quantum.h

@@ -95,6 +95,7 @@ void unregister_code16 (uint16_t code);
 
 #ifdef BACKLIGHT_ENABLE
 void backlight_init_ports(void);
+void backlight_task(void);
 
 #ifdef BACKLIGHT_BREATHING
 void breathing_enable(void);