Support Steam Deck controls directly through hidraw

This reads Steam Deck controls bypassing Steam Input. This allows for access to
motion controls as well as independent access to thumb sticks, trackpads, and
back grip buttons.

Source/Core/InputCommon/ControllerInterface/SteamDeck/SteamDeck.h

@@ -0,0 +1,13 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "InputCommon/ControllerInterface/InputBackend.h"
+
+#include <memory>
+
+namespace ciface::SteamDeck
+{
+std::unique_ptr<ciface::InputBackend> CreateInputBackend(ControllerInterface* controller_interface);
+}