build: add REUSE Compliance Check

In accordance with reuse requirements:
- Place each license file in the LICENSES/ directory
- Add missing SPDX-License-Identifier to files.
- Add .reuse/dep5 to bulk-license files

Fixes: #5887

Signed-off-by: Ruslan Mstoi <ruslan.mstoi@intel.com>

virtio-devices/src/balloon.rs

@@ -1,5 +1,7 @@
 // Copyright (c) 2020 Ant Financial
 //
+// SPDX-License-Identifier: Apache-2.0
+//
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at

virtio-devices/src/mem.rs

@@ -1,5 +1,7 @@
 // Copyright (c) 2020 Ant Financial
 //
+// SPDX-License-Identifier: Apache-2.0
+//
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at

virtio-devices/src/rng.rs

@@ -1,6 +1,8 @@
 // Copyright 2017 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
+//
+// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
 use super::Error as DeviceError;
 use super::{