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

@@ -1425,7 +1425,7 @@ 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;

Marlin/pins.h

@@ -321,6 +321,8 @@
 
 #if MOTHERBOARD == 33 || MOTHERBOARD == 34
 
+#define LARGE_FLASH        true
+
 #define X_STEP_PIN         54
 #define X_DIR_PIN          55
 #define X_ENABLE_PIN       38
@@ -789,6 +791,8 @@
  #endif
 #endif
 
+#define LARGE_FLASH true
+
 #define X_STEP_PIN 25
 #define X_DIR_PIN 23
 #define X_MIN_PIN 22
@@ -924,6 +928,8 @@
  #endif
 #endif
 
+#define LARGE_FLASH true
+
 #define X_STEP_PIN 25
 #define X_DIR_PIN 23
 #define X_MIN_PIN 15
@@ -993,6 +999,8 @@
 #error Oops!  Make sure you have 'Teensy++ 2.0' selected from the 'Tools -> Boards' menu.
 #endif
 
+#define LARGE_FLASH        true
+
 #define X_STEP_PIN          0
 #define X_DIR_PIN           1
 #define X_ENABLE_PIN       39
@@ -1326,6 +1334,8 @@
 #error Oops!  Make sure you have 'Arduino Mega 2560' selected from the 'Tools -> Boards' menu.
 #endif
 
+#define LARGE_FLASH true
+
 #define X_STEP_PIN 37
 #define X_DIR_PIN 48
 #define X_MIN_PIN 12
@@ -1401,7 +1411,7 @@
  #endif
 
 
-
+#define LARGE_FLASH        true
 
 #define X_STEP_PIN         26
 #define X_DIR_PIN          28