Fix behaviour for Armv8 targets without Neon

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/aesce.c b/library/aesce.c
index 11a22f6..ba09288 100644
--- a/library/aesce.c
+++ b/library/aesce.c
@@ -57,7 +57,7 @@
 
 #include "aesce.h"
 
-#if defined(MBEDTLS_ARCH_IS_ARMV8)
+#if defined(MBEDTLS_ARCH_IS_ARMV8) && defined(__ARM_NEON)
 
 /* Compiler version checks. */
 #if defined(__clang__)