Add LARGE_FLASH define and enable it for some of the beefier boards

The LARGE_FLASH flag allows superfluous features to be excluded
on boards with less memory

Marlin/Marlin_main.cpp

@@ -1424,8 +1424,8 @@ void process_commands()
       }
     }
     break;
-
-    #if defined(BEEPER) && BEEPER > -1
+    
+    #if defined(LARGE_FLASH) && LARGE_FLASH == true && defined(BEEPER) && BEEPER > -1
     case 300: // M300
     {
       int beepS = 1;