Move M163-M165 MIXING_EXTRUDER to cpp

Marlin/src/module/planner.cpp

@@ -80,6 +80,10 @@
   #include "../feature/baricuda.h"
 #endif
 
+#if ENABLED(MIXING_EXTRUDER)
+  #include "../feature/mixing.h"
+#endif
+
 Planner planner;
 
   // public:

Marlin/src/module/tool_change.cpp

@@ -42,6 +42,10 @@
   #include "../feature/snmm.h"
 #endif
 
+#if ENABLED(MIXING_EXTRUDER)
+  #include "../feature/mixing.h"
+#endif
+
 #if ENABLED(SWITCHING_EXTRUDER)
 
   #if EXTRUDERS > 3