HW: Don't be responsible for g_controller_interface

Currently, `g_controller_interface` is initialized and shut down by each
of `GCKeyboard`, `GCPad`, `Wiimote`, and `HotkeyManager`.

This 1) is weird conceptually, because it necessitates passing a pointer
to the native window to each of those classes, which don't need it, and
2) can cause issues when controller backends are initialized or shutdown
multiple times in succession.

Source/Core/Core/HW/GCKeyboard.h

@@ -12,7 +12,7 @@ struct KeyboardStatus;
 namespace Keyboard
 {
 void Shutdown();
-void Initialize(void* const hwnd);
+void Initialize();
 void LoadConfig();
 
 InputConfig* GetConfig();