Rename BEEPER to BEEPER_PIN

For consistency with other pins, allowing use of `PIN_EXISTS` macro.

Marlin/pins_RAMPS_13.h

@@ -159,7 +159,7 @@
     #endif
 
     #if ENABLED(REPRAP_DISCOUNT_SMART_CONTROLLER)
-      #define BEEPER 37
+      #define BEEPER_PIN 37
 
       #define BTN_EN1 31
       #define BTN_EN2 33
@@ -186,12 +186,12 @@
       #define SDCARDDETECT 49
       #define LCD_SDSS 53
       #define KILL_PIN 41
-      #define BEEPER 23
+      #define BEEPER_PIN 23
       #define DOGLCD_CS 29
       #define DOGLCD_A0 27
       #define LCD_PIN_BL 33
     #elif defined(MINIPANEL)
-       #define BEEPER 42
+       #define BEEPER_PIN 42
        // Pins for DOGM SPI LCD Support
        #define DOGLCD_A0  44
        #define DOGLCD_CS  66
@@ -211,9 +211,10 @@
        #define BTN_ENC 59  //the click switch
        //not connected to a pin
        #define SDCARDDETECT 49
+
     #else
-      // arduino pin which triggers an piezzo beeper
-      #define BEEPER 33  // Beeper on AUX-4
+
+      #define BEEPER_PIN 33  // Beeper on AUX-4
 
       // buttons are directly attached using AUX-2
       #if ENABLED(REPRAPWORLD_KEYPAD)
@@ -241,8 +242,8 @@
 
     #endif
   #else // !NEWPANEL (Old-style panel with shift register)
-    // Arduino pin to trigger a piezzo beeper
-    #define BEEPER 33   // No Beeper added
+
+    #define BEEPER_PIN 33   // No Beeper added
 
     // Buttons are attached to a shift register
     // Not wired yet