🩹 Use LCD_CONTRAST_INIT in pins files

Marlin/src/pins/mega/pins_GT2560_REV_A.h

 
       #define LCD_RESET_PIN                   16
 
-      #define LCD_CONTRAST_DEFAULT           220
+      #define LCD_CONTRAST_INIT              220
 
       #define LCD_BACKLIGHT_PIN               -1
     #else

Marlin/src/pins/ramps/pins_K8800.h

 
   #define LCD_CONTRAST_MIN                     0
   #define LCD_CONTRAST_MAX                   100
-  #define LCD_CONTRAST_DEFAULT                30
+  #define LCD_CONTRAST_INIT                   30
   //#define LCD_SCREEN_ROTATE                180  // 0, 90, 180, 270
 
   #if IS_NEWPANEL

Marlin/src/pins/stm32f4/pins_ARTILLERY_RUBY.h

       #define NEOPIXEL_PIN                  PB9
     #endif
 
-    #define LCD_CONTRAST_DEFAULT             255
+    #define LCD_CONTRAST_INIT                255
   #else
     #define LCD_PINS_RS                     PC15
     #define LCD_PINS_ENABLE                 PB6