Add GT2560 V4.x A20 variant pins

Marlin/src/core/boards.h

@@ -149,17 +149,18 @@
 #define BOARD_GT2560_REV_A            1314  // Geeetech GT2560 Rev A
 #define BOARD_GT2560_REV_A_PLUS       1315  // Geeetech GT2560 Rev A+ (with auto level probe)
 #define BOARD_GT2560_REV_B            1316  // Geeetech GT2560 Rev B
-#define BOARD_GT2560_V3               1317  // Geeetech GT2560 Rev B for A10(M/D)
-#define BOARD_GT2560_V4               1318  // Geeetech GT2560 Rev B for A10(M/D)
+#define BOARD_GT2560_V3               1317  // Geeetech GT2560 Rev B for A10(M/T/D)
+#define BOARD_GT2560_V4               1318  // Geeetech GT2560 Rev B for A10(M/T/D)
 #define BOARD_GT2560_V3_MC2           1319  // Geeetech GT2560 Rev B for Mecreator2
-#define BOARD_GT2560_V3_A20           1320  // Geeetech GT2560 Rev B for A20(M/D)
+#define BOARD_GT2560_V3_A20           1320  // Geeetech GT2560 Rev B for A20(M/T/D)
 #define BOARD_EINSTART_S              1321  // Einstart retrofit
 #define BOARD_WANHAO_ONEPLUS          1322  // Wanhao 0ne+ i3 Mini
 #define BOARD_LEAPFROG_XEED2015       1323  // Leapfrog Xeed 2015
 #define BOARD_PICA_REVB               1324  // PICA Shield (original version)
 #define BOARD_PICA                    1325  // PICA Shield (rev C or later)
 #define BOARD_INTAMSYS40              1326  // Intamsys 4.0 (Funmat HT)
 #define BOARD_MALYAN_M180             1327  // Malyan M180 Mainboard Version 2 (no display function, direct gcode only)
+#define BOARD_GT2560_V4_A20           1328  // Geeetech GT2560 Rev B for A20(M/T/D)
 
 //
 // ATmega1281, ATmega2561

Marlin/src/pins/mega/pins_GT2560_V4_A20.h

@@ -0,0 +1,43 @@
+/**
+ * Marlin 3D Printer Firmware
+ * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ */
+#pragma once
+
+/**
+ * Geeetech A20 GT2560 V4.x board pin assignments
+ */
+
+#define BOARD_INFO_NAME "GT2560 4.x"
+
+#define LCD_PINS_RS                            5
+#define LCD_PINS_ENABLE                       36
+#define LCD_PINS_D4                           21
+#define LCD_PINS_D7                            6
+
+#define SPEAKER                                  // The speaker can produce tones
+
+#if IS_NEWPANEL
+  #define BTN_EN1                             16
+  #define BTN_EN2                             17
+  #define BTN_ENC                             19
+#endif
+
+#include "pins_GT2560_V3.h"

Marlin/src/pins/pins.h

@@ -243,6 +243,8 @@
   #include "mega/pins_GT2560_REV_B.h"           // ATmega2560                             env:mega2560
 #elif MB(GT2560_V4)
   #include "mega/pins_GT2560_V4.h"              // ATmega2560                             env:mega2560
+  #elif MB(GT2560_V4_A20)
+  #include "mega/pins_GT2560_V4_A20.h"          // ATmega2560                             env:mega2560
 #elif MB(GT2560_V3_MC2)
   #include "mega/pins_GT2560_V3_MC2.h"          // ATmega2560                             env:mega2560
 #elif MB(GT2560_V3_A20)