Add copyright header to hash_wrappers.c

connectivity/mbedtls/source/hash_wrappers.c

@@ -1,3 +1,19 @@
+/* Copyright (c) 2018-2021 Arm Limited
+ * 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
+ *
+ *     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.
+ */
+
 #include "mbedtls/md2.h"
 #include "mbedtls/md4.h"
 #include "mbedtls/md5.h"