Move backward compatibility aliases to their own header

Move backward compatibility aliases to a separate header. Reserve
crypto_extra.h for implementation-specific extensions that we intend
to keep supporting.

This is better documentation for users. New users should simply ignore
backward compatibility aliases, and old users can look at
crypto_compat.h to see what is deprecated without bothering about new
features appearing in crypto_extra.h.

This facilitates maintenance because scripts such as
generate_psa_constants that want to ignore backward compability
aliases can simply exclude crypto_compat.h from their parsing.

include/psa/crypto_compat.h

@@ -0,0 +1,57 @@
+/**
+ * \file psa/crypto_compat.h
+ *
+ * \brief PSA cryptography module: Backward compatibility aliases
+ *
+ * \note This file may not be included directly. Applications must
+ * include psa/crypto.h.
+ */
+/*
+ *  Copyright (C) 2019, 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)
+ */
+
+#ifndef PSA_CRYPTO_COMPAT_H
+#define PSA_CRYPTO_COMPAT_H
+
+#include "mbedtls/platform_util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Deprecated PSA Crypto error code definitions
+ */
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+#define PSA_ERROR_UNKNOWN_ERROR \
+    MBEDTLS_DEPRECATED_NUMERIC_CONSTANT( PSA_ERROR_GENERIC_ERROR )
+#define PSA_ERROR_OCCUPIED_SLOT \
+    MBEDTLS_DEPRECATED_NUMERIC_CONSTANT( PSA_ERROR_ALREADY_EXISTS )
+#define PSA_ERROR_EMPTY_SLOT \
+    MBEDTLS_DEPRECATED_NUMERIC_CONSTANT( PSA_ERROR_DOES_NOT_EXIST )
+#define PSA_ERROR_INSUFFICIENT_CAPACITY \
+    MBEDTLS_DEPRECATED_NUMERIC_CONSTANT( PSA_ERROR_INSUFFICIENT_DATA )
+#define PSA_ERROR_TAMPERING_DETECTED \
+    MBEDTLS_DEPRECATED_NUMERIC_CONSTANT( PSA_ERROR_CORRUPTION_DETECTED )
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* PSA_CRYPTO_COMPAT_H */