ControllerInterface: devices population is now async so implement devices sorting priority

This helps us keeping the most important devices (e.g. Mouse and Keyboard) on the top
of the list of devices (they still are on all OSes supported by dolphin
and to make hotplug devices like DSU appear at the bottom.

Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.h

@@ -102,6 +102,7 @@ public:
 
   std::string GetName() const override;
   std::string GetSource() const override;
+  int GetSortPriority() const override;
 
 private:
   void UpdateCursorInput();