Move M300 to cpp

Marlin/src/Marlin.cpp

   return false;
 }
 
-#if HAS_BUZZER
-  #include "gcode/lcd/M300.h"
-#endif
-
 #if ENABLED(PIDTEMP)
   #include "gcode/config/M301.h"
 #endif

Marlin/src/gcode/gcode.cpp

 extern void gcode_M165();
 extern void gcode_M240();
 extern void gcode_M250();
-extern void gcode_M300();
 extern void gcode_M301();
 extern void gcode_M302();
 extern void gcode_M304();
       #endif
 
       #if HAS_BUZZER
-        case 300: // M300: Play beep tone
-          gcode_M300();
-          break;
-      #endif // HAS_BUZZER
+        case 300: M300(); break;  // M300: Play beep tone
+      #endif
 
       #if ENABLED(PIDTEMP)
         case 301: // M301: Set hotend PID parameters

Marlin/src/gcode/lcd/M300.h → Marlin/src/gcode/lcd/M300.cpp

  *
  */
 
+#include "../../inc/MarlinConfig.h"
+
+#if HAS_BUZZER
+
+#include "../gcode.h"
+
+#include "../../lcd/ultralcd.h" // i2c-based BUZZ
+#include "../../libs/buzzer.h"  // Buzzer, if possible
+
 /**
  * M300: Play beep sound S<frequency Hz> P<duration ms>
  */
-void gcode_M300() {
+void GcodeSuite::M300() {
   uint16_t const frequency = parser.ushortval('S', 260);
   uint16_t duration = parser.ushortval('P', 1000);
 
 
   BUZZ(duration, frequency);
 }
+
+#endif // HAS_BUZZER