Add a special input configuration dialog for the GameCube Mic

This is more logical as the mic is plugged into an EXI slot so it should be configured via the GameCube config dialog.  This also allows to pass the right port number for the new dialog.

Source/Core/DolphinWX/Input/MicButtonConfigDiag.h

@@ -0,0 +1,14 @@
+// Copyright 2016 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "DolphinWX/Input/InputConfigDiag.h"
+
+class MicButtonConfigDialog final : public InputConfigDialog
+{
+public:
+  MicButtonConfigDialog(wxWindow* parent, InputConfig& config, const wxString& name,
+                        int port_num = 0);
+};