Fix X2 enable with X_DUAL_STEPPER_DRIVERS

From #9286

Marlin/src/module/stepper.cpp

   #if HAS_X_ENABLE
     X_ENABLE_INIT;
     if (!X_ENABLE_ON) X_ENABLE_WRITE(HIGH);
-    #if ENABLED(DUAL_X_CARRIAGE) && HAS_X2_ENABLE
+    #if (ENABLED(DUAL_X_CARRIAGE) || ENABLED(X_DUAL_STEPPER_DRIVERS)) && HAS_X2_ENABLE
       X2_ENABLE_INIT;
       if (!X_ENABLE_ON) X2_ENABLE_WRITE(HIGH);
     #endif