Revert "Kernel/Storage: Remove the ramdisk implementation"

This reverts commit 4e0f85432a as the
ramdisk code is useful for the bring-up of the aarch64 port. Once the
kernel supports better ram-based filesystems, this code will be removed
again.

Kernel/Storage/Ramdisk/Controller.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/OwnPtr.h>
+#include <AK/Types.h>
+#include <Kernel/Library/LockRefPtr.h>
+#include <Kernel/Storage/Ramdisk/Device.h>
+#include <Kernel/Storage/StorageController.h>
+#include <Kernel/Storage/StorageDevice.h>
+
+namespace Kernel {
+
+class AsyncBlockDeviceRequest;
+
+class RamdiskController final : public StorageController {
+public:
+    static NonnullLockRefPtr<RamdiskController> initialize();
+    virtual ~RamdiskController() override;
+
+    virtual LockRefPtr<StorageDevice> device(u32 index) const override;
+    virtual bool reset() override;
+    virtual bool shutdown() override;
+    virtual size_t devices_count() const override;
+    virtual void complete_current_request(AsyncDeviceRequest::RequestResult) override;
+
+private:
+    RamdiskController();
+
+    NonnullLockRefPtrVector<RamdiskDevice> m_devices;
+};
+}