Add EXTRA_FAN_SPEED feature

Based on #7883 by @studiodyne

Marlin/src/Marlin.cpp

@@ -165,6 +165,10 @@ bool axis_homed[XYZ] = { false }, axis_known_position[XYZ] = { false };
 
 #if FAN_COUNT > 0
   int16_t fanSpeeds[FAN_COUNT] = { 0 };
+  #if ENABLED(EXTRA_FAN_SPEEDS)
+    int16_t old_fanSpeeds[FAN_COUNT],
+            new_fanSpeeds[FAN_COUNT];
+  #endif
   #if ENABLED(PROBING_FANS_OFF)
     bool fans_paused = false;
     int16_t paused_fanSpeeds[FAN_COUNT] = { 0 };