Kernel: Move all Graphics-related code into Devices/GPU directory

Like the HID, Audio and Storage subsystem, the Graphics subsystem (which
handles GPUs technically) exposes unix device files (typically in /dev).
To ensure consistency across the repository, move all related files to a
new directory under Kernel/Devices called "GPU".

Also remove the redundant "GPU" word from the VirtIO driver directory,
and the word "Graphics" from GraphicsManagement.{h,cpp} filenames.

Kernel/Graphics/Intel/NativeGraphicsAdapter.h

@@ -1,38 +0,0 @@
-/*
- * Copyright (c) 2021, Liav A. <liavalb@hotmail.co.il>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#pragma once
-
-#include <AK/Types.h>
-#include <Kernel/Bus/PCI/Device.h>
-#include <Kernel/Graphics/Definitions.h>
-#include <Kernel/Graphics/Intel/DisplayConnectorGroup.h>
-#include <Kernel/Graphics/Intel/NativeDisplayConnector.h>
-#include <Kernel/Memory/PhysicalAddress.h>
-#include <LibEDID/EDID.h>
-
-namespace Kernel {
-
-class IntelNativeGraphicsAdapter final
-    : public GenericGraphicsAdapter
-    , public PCI::Device {
-
-public:
-    static ErrorOr<bool> probe(PCI::DeviceIdentifier const&);
-    static ErrorOr<NonnullLockRefPtr<GenericGraphicsAdapter>> create(PCI::DeviceIdentifier const&);
-
-    virtual ~IntelNativeGraphicsAdapter() = default;
-
-    virtual StringView device_name() const override { return "IntelNativeGraphicsAdapter"sv; }
-
-private:
-    ErrorOr<void> initialize_adapter();
-
-    explicit IntelNativeGraphicsAdapter(PCI::DeviceIdentifier const&);
-
-    LockRefPtr<IntelDisplayConnectorGroup> m_connector_group;
-};
-}