Init serial ports first (#20944)

Marlin/src/MarlinCore.cpp

   #endif
   #define SETUP_RUN(C) do{ SETUP_LOG(STRINGIFY(C)); C; }while(0)
 
+  MYSERIAL0.begin(BAUDRATE);
+  millis_t serial_connect_timeout = millis() + 1000UL;
+  while (!MYSERIAL0.connected() && PENDING(millis(), serial_connect_timeout)) { /*nada*/ }
+
+  #if HAS_MULTI_SERIAL && !HAS_ETHERNET
+    MYSERIAL1.begin(BAUDRATE);
+    serial_connect_timeout = millis() + 1000UL;
+    while (!MYSERIAL1.connected() && PENDING(millis(), serial_connect_timeout)) { /*nada*/ }
+  #endif
+  SERIAL_ECHOLNPGM("start");
+
   // Set up these pins early to prevent suicide
   #if HAS_KILL
     SETUP_LOG("KILL_PIN");
     #endif
   #endif
 
-  MYSERIAL0.begin(BAUDRATE);
-  millis_t serial_connect_timeout = millis() + 1000UL;
-  while (!MYSERIAL0.connected() && PENDING(millis(), serial_connect_timeout)) { /*nada*/ }
-
-  #if HAS_MULTI_SERIAL && !HAS_ETHERNET
-    MYSERIAL1.begin(BAUDRATE);
-    serial_connect_timeout = millis() + 1000UL;
-    while (!MYSERIAL1.connected() && PENDING(millis(), serial_connect_timeout)) { /*nada*/ }
-  #endif
-  SERIAL_ECHOLNPGM("start");
-
   #if BOTH(HAS_TFT_LVGL_UI, MKS_WIFI_MODULE)
     mks_esp_wifi_init();
     WIFISERIAL.begin(WIFI_BAUDRATE);