Added support for local multiplayer

src/xenia/hid/input_system.h

@@ -44,10 +44,15 @@ class InputSystem {
   X_RESULT GetKeystroke(uint32_t user_index, uint32_t flags,
                         X_INPUT_KEYSTROKE* out_keystroke);
 
+  void UpdateUsedSlot(uint8_t slot, bool connected);
+  uint8_t GetConnectedSlots() const { return connected_slot; }
+
  private:
   xe::ui::Window* window_ = nullptr;
 
   std::vector<std::unique_ptr<InputDriver>> drivers_;
+
+  uint8_t connected_slot = 0b0001;
 };
 
 }  // namespace hid