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/Wiimote/WiimoteController.cpp

@@ -321,6 +321,12 @@ std::string Device::GetSource() const
   return SOURCE_NAME;
 }
 
+// Always add these at the end, given their hotplug nature
+int Device::GetSortPriority() const
+{
+  return -1;
+}
+
 void Device::RunTasks()
 {
   if (IsPerformingTask())