Enable PSA Crypto APIs by default

Since this example is not useful without PSA Crypto APIs, enable PSA APIs
by default via an Mbed TLS user configuration file.

Author: Patater

mbed_app.json

@@ -4,6 +4,9 @@
              "platform.stdio-convert-newlines": true,
              "target.extra_labels_add": ["PSA"]
         }
-    }
+    },
+    "macros": [
+        "MBEDTLS_USER_CONFIG_FILE=\"mbedtls_user_config.h\""
+    ]
 }
 

mbedtls_user_config.h

@@ -0,0 +1,21 @@
+/*
+ *  Copyright (C) 2006-2018, Arm Limited, All Rights Reserved
+ *  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.
+ *
+ *  This file is part of Mbed TLS (https://tls.mbed.org)
+ */
+
+/* Enable PSA APIs, which this example depends on. */
+#define MBEDTLS_PSA_CRYPTO_C