Add BOARD_PREINIT (for Longer3D open drain pins) (#21159)

Marlin/src/MarlinCore.cpp

@@ -870,6 +870,9 @@ inline void tmc_standby_setup() {
  *    • Max7219
  */
 void setup() {
+  #ifdef BOARD_PREINIT
+    BOARD_PREINIT(); // Low-level init (before serial init)
+  #endif
 
   tmc_standby_setup();  // TMC Low Power Standby pins must be set early or they're not usable