Support for MKS BASE 1.0 board

Marlin/boards.h

 #define BOARD_ELEFU_3           21   // Elefu Ra Board (v3)
 #define BOARD_5DPRINT           88   // 5DPrint D8 Driver Board
 #define BOARD_LEAPFROG          999  // Leapfrog
+#define BOARD_MKS_BASE          40   // MKS BASE 1.0
 #define BOARD_WITBOX            41   // bq WITBOX
 #define BOARD_HEPHESTOS         42   // bq Prusa i3 Hephestos
 #define BOARD_BAM_DICE          401  // 2PrintBeta BAM&DICE with STK drivers

Marlin/pins_MKS_BASE.h

+/**
+ * MKS BASE 1.0 – Arduino Mega2560 with RAMPS v1.4 pin assignments
+ */
+
+#include "pins_RAMPS_13.h"
+
+#undef FAN_PIN
+#define FAN_PIN             9 // (Sprinter config)
+
+#undef HEATER_1_PIN
+#define HEATER_1_PIN        7