Set stepper directions after M501/M502

See https://github.com/MarlinFirmware/Marlin/issues/11103#issuecomment-421387611

Co-Authored-By: tcm0116 <tcm0116@users.noreply.github.com>

Marlin/stepper.h

@@ -467,6 +467,9 @@ class Stepper {
     // Set direction bits for all steppers
     static void set_directions();
 
+    // Allow reset_stepper_drivers to access private set_directions
+    friend void reset_stepper_drivers();
+
     FORCE_INLINE static uint32_t calc_timer_interval(uint32_t step_rate, uint8_t scale, uint8_t* loops) {
       uint32_t timer;