Enable PSA Crypto APIs by default

Since this example is not useful without PSA Crypto APIs, enable PSA
Crypto APIs by default via an Mbed TLS user configuration file, along
with a default implmentation of the PSA Entropy Injection API that
uses PSA storage (ITS).

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 +1,32 @@
+/*
+ *  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. */
+#if !defined(MBEDTLS_PSA_CRYPTO_C)
+#   define MBEDTLS_PSA_CRYPTO_C
+#endif
+
+/* Enable the default implementation of the PSA entropy injection API if we are
+ * building for an SPE. */
+#if defined(COMPONENT_PSA_SRV_IMPL) || defined(COMPONENT_PSA_SRV_EMUL)
+#   define MBEDTLS_ENTROPY_NV_SEED
+#   define MBEDTLS_PSA_HAS_ITS_IO
+#   define MBEDTLS_PLATFORM_NV_SEED_READ_MACRO mbed_default_seed_read
+#   define MBEDTLS_PLATFORM_NV_SEED_WRITE_MACRO mbed_default_seed_write
+#endif