Add support for MF68 replacement PCB for Magicforce 68 (#1698)

* Port TMK code for MF68

* Change KEYMAP to KC_KEYMAP and add macro

keyboards/mf68/mf68.c

@@ -0,0 +1,8 @@
+#include "mf68.h"
+
+void matrix_init_kb(void) {
+	// put your keyboard start-up code here
+	// runs once when the firmware starts up
+
+	matrix_init_user();
+}