Add a reference configuration without any asymmetric cryptography

Add a reference configuration with most symmetric cryptographic
algorithms enabled, but without any asymmetric cryptography. This
checks that we don't have spurious unexpected dependencies on
asymmetric-only modules such as bignum.

Keep HAVE_ASM disabled because it's platform-specific.

Keep HAVEGE disabled because it's untested and not recommended.

Keep MEMORY_BUFFER_ALLOC out because it isn't related to cryptography
at all and it makes memory sanitizers ineffective.

Keep THREADING disabled because it requires special build options.
diff --git a/configs/config-symmetric-only.h b/configs/config-symmetric-only.h
new file mode 100644
index 0000000..94e80ab
--- /dev/null
+++ b/configs/config-symmetric-only.h
@@ -0,0 +1,99 @@
+/**
+ * \file config-symmetric-only.h
+ *
+ * \brief Configuration without any asymmetric cryptography.
+ */
+/*
+ *  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 MBEDTLS_CONFIG_H
+#define MBEDTLS_CONFIG_H
+
+/* System support */
+//#define MBEDTLS_HAVE_ASM
+#define MBEDTLS_HAVE_TIME
+#define MBEDTLS_HAVE_TIME_DATE
+
+/* Mbed Crypto feature support */
+#define MBEDTLS_CIPHER_MODE_CBC
+#define MBEDTLS_CIPHER_MODE_CFB
+#define MBEDTLS_CIPHER_MODE_CTR
+#define MBEDTLS_CIPHER_MODE_OFB
+#define MBEDTLS_CIPHER_MODE_XTS
+#define MBEDTLS_CIPHER_PADDING_PKCS7
+#define MBEDTLS_CIPHER_PADDING_ONE_AND_ZEROS
+#define MBEDTLS_CIPHER_PADDING_ZEROS_AND_LEN
+#define MBEDTLS_CIPHER_PADDING_ZEROS
+#define MBEDTLS_ERROR_STRERROR_DUMMY
+#define MBEDTLS_FS_IO
+#define MBEDTLS_ENTROPY_NV_SEED
+#define MBEDTLS_SELF_TEST
+#define MBEDTLS_USE_PSA_CRYPTO
+#define MBEDTLS_VERSION_FEATURES
+
+/* Mbed Crypto modules */
+#define MBEDTLS_AES_C
+#define MBEDTLS_ARC4_C
+#define MBEDTLS_ASN1_PARSE_C
+#define MBEDTLS_ASN1_WRITE_C
+#define MBEDTLS_BASE64_C
+#define MBEDTLS_BLOWFISH_C
+#define MBEDTLS_CAMELLIA_C
+#define MBEDTLS_ARIA_C
+#define MBEDTLS_CCM_C
+#define MBEDTLS_CHACHA20_C
+#define MBEDTLS_CHACHAPOLY_C
+#define MBEDTLS_CIPHER_C
+#define MBEDTLS_CMAC_C
+#define MBEDTLS_CTR_DRBG_C
+#define MBEDTLS_DES_C
+#define MBEDTLS_ENTROPY_C
+#define MBEDTLS_ERROR_C
+#define MBEDTLS_GCM_C
+//#define MBEDTLS_HAVEGE_C
+#define MBEDTLS_HKDF_C
+#define MBEDTLS_HMAC_DRBG_C
+#define MBEDTLS_NIST_KW_C
+#define MBEDTLS_MD_C
+#define MBEDTLS_MD2_C
+#define MBEDTLS_MD4_C
+#define MBEDTLS_MD5_C
+#define MBEDTLS_OID_C
+#define MBEDTLS_PEM_PARSE_C
+#define MBEDTLS_PEM_WRITE_C
+#define MBEDTLS_PKCS5_C
+#define MBEDTLS_PKCS12_C
+#define MBEDTLS_PLATFORM_C
+#define MBEDTLS_POLY1305_C
+#define MBEDTLS_PSA_CRYPTO_C
+#define MBEDTLS_PSA_CRYPTO_SE_C
+#define MBEDTLS_PSA_CRYPTO_STORAGE_C
+#define MBEDTLS_PSA_ITS_FILE_C
+#define MBEDTLS_RIPEMD160_C
+#define MBEDTLS_SHA1_C
+#define MBEDTLS_SHA256_C
+#define MBEDTLS_SHA512_C
+//#define MBEDTLS_THREADING_C
+#define MBEDTLS_TIMING_C
+#define MBEDTLS_VERSION_C
+#define MBEDTLS_XTEA_C
+
+#include "check_config.h"
+
+#endif /* MBEDTLS_CONFIG_H */