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/scripts/config.py b/scripts/config.py
index 6d5edc7..0ab1e39 100755
--- a/scripts/config.py
+++ b/scripts/config.py
@@ -198,6 +198,7 @@
     'MBEDTLS_PSA_CRYPTO_SPM', # platform dependency (PSA SPM)
     'MBEDTLS_PSA_INJECT_ENTROPY', # build dependency (hook functions)
     'MBEDTLS_RSA_NO_CRT', # influences the use of RSA in X.509 and TLS
+    'MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY', # interacts with *_USE_A64_CRYPTO_ONLY
     'MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN', # build dependency (clang+memsan)
     'MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND', # build dependency (valgrind headers)
     'MBEDTLS_X509_REMOVE_INFO', # removes a feature