boot: Update copyrights and licenses

To make contributions easier, place explicit copyrights by the major
contributors, along with an SPDX license identifier.  Files that came
from the mynewt project, which was an Apache project will retain the
Apache project license text, although this does not apply to new
contributions, which are being made by individual contributors.

Hopefully, this will keep everyone happy, but allow contributors that
need to add an explicit copyright to have a place they can add that.

Fixes #501

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/boot/bootutil/src/encrypted.c b/boot/bootutil/src/encrypted.c
index abc9fdd..6104397 100644
--- a/boot/bootutil/src/encrypted.c
+++ b/boot/bootutil/src/encrypted.c
@@ -1,20 +1,8 @@
 /*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you 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
+ * SPDX-License-Identifier: Apache-2.0
  *
- *  http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
+ * Copyright (c) 2018-2019 JUUL Labs
+ * Copyright (c) 2019 Arm Limited
  */
 
 #include "mcuboot_config/mcuboot_config.h"