Pre-override of ST7920 delays before HAL.h

Marlin/src/HAL/HAL_LPC1768/HAL.h

 #include "HAL_timers.h"
 #include "HardwareSerial.h"
 
-#define ST7920_DELAY_1 DELAY_NS(600)
-#define ST7920_DELAY_2 DELAY_NS(750)
-#define ST7920_DELAY_3 DELAY_NS(750)
+#ifndef ST7920_DELAY_1
+  #define ST7920_DELAY_1 DELAY_NS(600)
+#endif
+#ifndef ST7920_DELAY_2
+  #define ST7920_DELAY_2 DELAY_NS(750)
+#endif
+#ifndef ST7920_DELAY_3
+  #define ST7920_DELAY_3 DELAY_NS(750)
+#endif
 
 extern HalSerial usb_serial;