Kernel: Move the Storage directory to be a new directory under Devices

The Storage subsystem, like the Audio and HID subsystems, exposes Unix
device files (for example, in the /dev directory). To ensure consistency
across the repository, we should make the Storage subsystem to reside in
the Kernel/Devices directory like the two other mentioned subsystems.

Kernel/Devices/Storage/DiskPartition.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <Kernel/Devices/BlockDevice.h>
+#include <Kernel/Library/LockRefPtr.h>
+#include <Kernel/Library/LockWeakPtr.h>
+#include <LibPartition/DiskPartitionMetadata.h>
+
+namespace Kernel {
+
+class DiskPartition final : public BlockDevice {
+    friend class DeviceManagement;
+
+public:
+    static NonnullLockRefPtr<DiskPartition> create(BlockDevice&, MinorNumber, Partition::DiskPartitionMetadata);
+    virtual ~DiskPartition();
+
+    virtual void start_request(AsyncBlockDeviceRequest&) override;
+
+    // ^BlockDevice
+    virtual ErrorOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) override;
+    virtual bool can_read(OpenFileDescription const&, u64) const override;
+    virtual ErrorOr<size_t> write(OpenFileDescription&, u64, UserOrKernelBuffer const&, size_t) override;
+    virtual bool can_write(OpenFileDescription const&, u64) const override;
+
+    Partition::DiskPartitionMetadata const& metadata() const;
+
+private:
+    DiskPartition(BlockDevice&, MinorNumber, Partition::DiskPartitionMetadata);
+    virtual StringView class_name() const override;
+
+    LockWeakPtr<BlockDevice> m_device;
+    Partition::DiskPartitionMetadata m_metadata;
+};
+
+}