Fix serial.h including itself

Marlin/src/core/serial.cpp

 
 #if ENABLED(DEBUG_LEVELING_FEATURE)
 
+  #include "enum.h"
+
   void print_xyz(const char* prefix, const char* suffix, const float x, const float y, const float z) {
     serialprintPGM(prefix);
     SERIAL_CHAR('(');

Marlin/src/core/serial.h

 #ifndef __SERIAL_H__
 #define __SERIAL_H__
 
-#include "../inc/MarlinConfig.h"
+#include "../inc/MarlinConfigPre.h"
+#include HAL_PATH(../HAL, HAL.h)
 
 /**
  * Define debug bit-masks