Fix Ender 4 / CR-8 compilation

- Assign 243 (like EFB) as Ender-4/CR-8 board ID
- Add to `Makefile`
- Add to `pins.h`

Marlin/src/Makefile

@@ -148,6 +148,9 @@ MCU              ?= atmega2560
 else ifeq  ($(HARDWARE_MOTHERBOARD),48)
 HARDWARE_VARIANT ?= arduino
 MCU              ?= atmega2560
+else ifeq  ($(HARDWARE_MOTHERBOARD),243)
+HARDWARE_VARIANT ?= arduino
+MCU              ?= atmega2560
 
 #Gen6
 else ifeq  ($(HARDWARE_MOTHERBOARD),5)

Marlin/src/core/boards.h

@@ -76,6 +76,7 @@
 #define BOARD_BQ_ZUM_MEGA_3D    503   // bq ZUM Mega 3D
 #define BOARD_MAKEBOARD_MINI    431   // MakeBoard Mini v2.1.2 is a control board sold by MicroMake
 #define BOARD_TRIGORILLA        343   // TriGorilla Anycubic version 1.3 based on RAMPS EFB
+#define BOARD_RAMPS_ENDER_4     243   // Creality: Ender-4, CR-8
 
 //
 // Other ATmega1280, ATmega2560

Marlin/src/pins/pins.h

@@ -175,6 +175,8 @@
   #include "pins_GT2560_REV_A.h"      // ATmega1280, ATmega2560
 #elif MB(GT2560_REV_A_PLUS)
   #include "pins_GT2560_REV_A_PLUS.h" // ATmega1280, ATmega2560
+#elif MB(RAMPS_ENDER_4)
+  #include "pins_RAMPS_ENDER_4.h"     // ATmega2560
 
 //
 // ATmega1281, ATmega2561