HAL support for 8s watchdog

Marlin/src/HAL/LPC1768/watchdog.cpp

@@ -28,6 +28,8 @@
 #include <lpc17xx_wdt.h>
 #include "watchdog.h"
 
+#define WDT_TIMEOUT_US TERN(WATCHDOG_DURATION_8S, 8000000, 4000000) // 4 or 8 second timeout
+
 void watchdog_init() {
   #if ENABLED(WATCHDOG_RESET_MANUAL)
     // We enable the watchdog timer, but only for the interrupt.
@@ -52,7 +54,7 @@ void watchdog_init() {
   #else
     WDT_Init(WDT_CLKSRC_IRC, WDT_MODE_RESET);
   #endif
-  WDT_Start(WDT_TIMEOUT);
+  WDT_Start(WDT_TIMEOUT_US);
 }
 
 void HAL_watchdog_refresh() {