Move M400 to cpp

Marlin/src/Marlin.cpp

   return false;
 }
 
-#include "gcode/control/M400.h"
-
 #if HAS_BED_PROBE
   #include "gcode/probe/M401_M402.h"
 #endif

Marlin/src/gcode/control/M400.h → Marlin/src/gcode/control/M400.cpp

  *
  */
 
+#include "../gcode.h"
+#include "../../module/stepper.h"
+
 /**
  * M400: Finish all moves
  */
-void gcode_M400() {
+void GcodeSuite::M400() {
 
   stepper.synchronize();
 

Marlin/src/gcode/gcode.cpp

 extern void gcode_M350();
 extern void gcode_M351();
 extern void gcode_M355();
-extern void gcode_M400();
 extern void gcode_M401();
 extern void gcode_M402();
 extern void gcode_M428();
         case 381: M381(); break;  // M381: Disable all solenoids
       #endif
 
-      case 400: // M400: Finish all moves
-        gcode_M400();
-        break;
+      case 400: M400(); break;    // M400: Finish all moves
 
       #if HAS_BED_PROBE
         case 401: // M401: Deploy probe