fix TMC2208 boot loop with SW UART

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

Marlin/src/Marlin.cpp

@@ -873,6 +873,10 @@ void setup() {
 
   setup_killpin();
   
+  #if HAS_DRIVER(TMC2208)
+    tmc2208_serial_begin();
+  #endif
+  
   setup_powerhold();
 
   #if HAS_STEPPER_RESET
@@ -904,9 +908,6 @@ void setup() {
     #endif
     tmc_init_cs_pins();
   #endif
-  #if HAS_DRIVER(TMC2208)
-    tmc2208_serial_begin();
-  #endif
 
   #ifdef BOARD_INIT
     BOARD_INIT();