Set auto fan pins to OUTPUT during init

Fixes the problem of these pins being left in INPUT state, as described
in #1497

Marlin/temperature.cpp

@@ -374,7 +374,6 @@ void setExtruderAutoFanState(int pin, bool state)
 {
   unsigned char newFanSpeed = (state != 0) ? EXTRUDER_AUTO_FAN_SPEED : 0;
   // this idiom allows both digital and PWM fan outputs (see M42 handling).
-  pinMode(pin, OUTPUT);
   digitalWrite(pin, newFanSpeed);
   analogWrite(pin, newFanSpeed);
 }
@@ -918,6 +917,19 @@ void tp_init() {
     ANALOG_SELECT(FILWIDTH_PIN);
   #endif
   
+  #if HAS_AUTO_FAN_0
+    pinMode(EXTRUDER_0_AUTO_FAN_PIN, OUTPUT);
+  #endif
+  #if HAS_AUTO_FAN_1 && (EXTRUDER_1_AUTO_FAN_PIN != EXTRUDER_0_AUTO_FAN_PIN)
+    pinMode(EXTRUDER_1_AUTO_FAN_PIN, OUTPUT);
+  #endif
+  #if HAS_AUTO_FAN_2 && (EXTRUDER_2_AUTO_FAN_PIN != EXTRUDER_0_AUTO_FAN_PIN) && (EXTRUDER_2_AUTO_FAN_PIN != EXTRUDER_1_AUTO_FAN_PIN)
+    pinMode(EXTRUDER_2_AUTO_FAN_PIN, OUTPUT);
+  #endif
+  #if HAS_AUTO_FAN_3 && (EXTRUDER_3_AUTO_FAN_PIN != EXTRUDER_0_AUTO_FAN_PIN) && (EXTRUDER_3_AUTO_FAN_PIN != EXTRUDER_1_AUTO_FAN_PIN) && (EXTRUDER_3_AUTO_FAN_PIN != EXTRUDER_2_AUTO_FAN_PIN)
+    pinMode(EXTRUDER_3_AUTO_FAN_PIN, OUTPUT);
+  #endif
+
   // Use timer0 for temperature measurement
   // Interleave temperature interrupt with millies interrupt
   OCR0B = 128;