Fix behaviour for Armv8 targets without Neon

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/aesce.h b/library/aesce.h
index 97e2424..2cec2f3 100644
--- a/library/aesce.h
+++ b/library/aesce.h
@@ -2,7 +2,7 @@
  * \file aesce.h
  *
  * \brief Support hardware AES acceleration on Armv8-A processors with
- *        the Armv8-A Cryptographic Extension in AArch64 execution state.
+ *        the Armv8-A Cryptographic Extension.
  *
  * \warning These functions are only for internal use by other library
  *          functions; you must not call them directly.
@@ -31,7 +31,7 @@
 #include "mbedtls/aes.h"
 
 
-#if defined(MBEDTLS_AESCE_C) && defined(MBEDTLS_ARCH_IS_ARMV8)
+#if defined(MBEDTLS_AESCE_C) && defined(MBEDTLS_ARCH_IS_ARMV8) && defined(__ARM_NEON)
 
 #define MBEDTLS_AESCE_HAVE_CODE
 
@@ -128,6 +128,12 @@
 }
 #endif
 
-#endif /* MBEDTLS_AESCE_C && MBEDTLS_ARCH_IS_ARM64 */
+#else
+
+#if defined(MBEDTLS_AES_USE_HARDWARE_ONLY)
+#error "AES hardware acceleration not supported on this platform"
+#endif
+
+#endif /* MBEDTLS_AESCE_C && MBEDTLS_ARCH_IS_ARMV8 && __ARM_NEON */
 
 #endif /* MBEDTLS_AESCE_H */