Bed Heater monitoring in Controller Fan

In some cases the Bed Heater FET heats up more then stepper drivers, so
this change add the bed monitoring to the controller fan. As soon as the
bed heater is turned on, the controller fan will run as well.

Marlin/Marlin_main.cpp

   {
     lastMotorCheck = millis();
 
-    if(!READ(X_ENABLE_PIN) || !READ(Y_ENABLE_PIN) || !READ(Z_ENABLE_PIN)
+    if(!READ(X_ENABLE_PIN) || !READ(Y_ENABLE_PIN) || !READ(Z_ENABLE_PIN) || (soft_pwm_bed > 0)
     #if EXTRUDERS > 2
        || !READ(E2_ENABLE_PIN)
     #endif

Marlin/temperature.cpp

 #ifdef FAN_SOFT_PWM
   unsigned char fanSpeedSoftPwm;
 #endif
+
+unsigned char soft_pwm_bed;
   
 #ifdef BABYSTEPPING
   volatile int babystepsTodo[3]={0,0,0};
 	static unsigned long  previous_millis_bed_heater;
 #endif //PIDTEMPBED
   static unsigned char soft_pwm[EXTRUDERS];
-  static unsigned char soft_pwm_bed;
+
 #ifdef FAN_SOFT_PWM
   static unsigned char soft_pwm_fan;
 #endif

Marlin/temperature.h

   extern float redundant_temperature;
 #endif
 
+#if defined(CONTROLLERFAN_PIN) && CONTROLLERFAN_PIN > -1
+  extern unsigned char soft_pwm_bed;
+#endif
+
 #ifdef PIDTEMP
   extern float Kp,Ki,Kd,Kc;
   float scalePID_i(float i);