Restructure the way driver contexts are declared

Drivers (both built-in and external) need to declare their context
structures in a way such that they are accessible by the
to-be-autogenerated crypto_driver_contexts.h file. That file lives in
include/psa, which means all builtin driver context structure
declarations also need to live in include/psa.

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>

include/psa/crypto_driver_contexts.h

@@ -0,0 +1,51 @@
+/*
+ *  Declaration of context structures for use with the PSA driver wrapper
+ *  interface.
+ *
+ *  Warning: This file will be auto-generated in the future.
+ */
+/*  Copyright The Mbed TLS Contributors
+ *  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.
+ */
+
+#ifndef PSA_CRYPTO_DRIVER_CONTEXTS_H
+#define PSA_CRYPTO_DRIVER_CONTEXTS_H
+
+#include "psa/crypto.h"
+#include "psa/crypto_driver_common.h"
+
+/* Include the context structure definitions for those drivers that were
+ * declared during the autogeneration process. */
+
+/* Include the context structure definitions for the Mbed TLS software drivers */
+#include "psa/crypto_builtin_hash.h"
+
+/* Define the context to be used for an operation that is executed through the
+ * PSA Driver wrapper layer as the union of all possible driver's contexts.
+ *
+ * The union members are the driver's context structures, and the member names
+ * are formatted as `'drivername'_ctx`. This allows for procedural generation
+ * of both this file and the content of psa_crypto_driver_wrappers.c */
+
+typedef union {
+    unsigned dummy; /* Make sure this structure is always non-empty */
+    mbedtls_psa_hash_operation_t mbedtls_ctx;
+#if defined(PSA_CRYPTO_DRIVER_TEST)
+    mbedtls_transparent_test_driver_hash_operation_t test_ctx;
+#endif
+} psa_driver_hash_context_t;
+
+#endif /* PSA_CRYPTO_DRIVER_CONTEXTS_H */
+/* End of automatically generated file. */