Make SHA256 depend on Armv8, not aarch64

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index e18e9a5..1580707 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -865,9 +865,8 @@
 
 #endif
 
-#if defined(MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY) && \
-    !defined(__aarch64__) && !defined(_M_ARM64)
-#error "MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY defined on non-Aarch64 system"
+#if defined(MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY) && !defined(MBEDTLS_ARCH_IS_ARMV8)
+#error "MBEDTLS_SHA256_USE_A64_CRYPTO_ONLY defined on non-Armv8 system"
 #endif
 
 /* TLS 1.3 requires separate HKDF parts from PSA,