SECLIB-667: Accelerate SHA-256 with A64 crypto extensions

Provide an additional pair of #defines, MBEDTLS_SHA256_USE_A64_CRYPTO_IF_PRESENT
and MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY. At most one of them may be
specified. If used, it is necessary to compile with -march=armv8-a+crypto.

The MBEDTLS_SHA256_PROCESS_ALT and MBEDTLS_SHA256_ALT mechanisms
continue to work, and are mutually exclusive with A64_CRYPTO.

There should be minimal code size impact if no A64_CRYPTO option is set.

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index d7cc7bc..a645819 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -592,6 +592,28 @@
 #error "MBEDTLS_SHA256_C defined without MBEDTLS_SHA224_C"
 #endif
 
+#if defined(MBEDTLS_SHA256_USE_A64_CRYPTO_IF_PRESENT) && \
+    defined(MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY)
+#error "Must only define one of MBEDTLS_SHA256_USE_A64_CRYPTO_*"
+#endif
+
+#if defined(MBEDTLS_SHA256_USE_A64_CRYPTO_IF_PRESENT) || \
+    defined(MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY)
+#if !defined(MBEDTLS_SHA256_C)
+#error "MBEDTLS_SHA256_USE_A64_CRYPTO_* defined without MBEDTLS_SHA256_C"
+#endif
+#if defined(MBEDTLS_SHA256_ALT) || defined(MBEDTLS_SHA256_PROCESS_ALT)
+#error "MBEDTLS_SHA256_*ALT can't be used with MBEDTLS_SHA256_USE_A64_CRYPTO_*"
+#endif
+#if defined(__aarch64__) && !defined(__ARM_FEATURE_CRYPTO)
+#error "Must use minimum -march=armv8-a+crypto for MBEDTLS_SHA256_USE_A64_CRYPTO_*"
+#endif
+#endif
+
+#if defined(MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY) && !defined(__aarch64__)
+#error "MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY defined on non-Aarch64 system"
+#endif
+
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && ( !defined(MBEDTLS_SHA1_C) &&     \
     !defined(MBEDTLS_SHA256_C) && !defined(MBEDTLS_SHA512_C) )
 #error "MBEDTLS_SSL_PROTO_TLS1_2 defined, but not all prerequisites"