fix TMC2208 boot loop with SW UART (#14135)

Need stepper .begin() before calling susbequent .push()

Marlin/src/Marlin.cpp

   #endif
 
   setup_killpin();
-
+  
+  #if HAS_DRIVER(TMC2208)
+    tmc2208_serial_begin();
+  #endif
+  
   setup_powerhold();
 
   #if HAS_STEPPER_RESET
     #endif
     tmc_init_cs_pins();
   #endif
-  #if HAS_DRIVER(TMC2208)
-    tmc2208_serial_begin();
-  #endif
 
   #ifdef BOARD_INIT
     BOARD_INIT();