avx512: add basic functions to simd_utils

Extends the m512 type to use avx512 and also changes required
for limex.

cmake/config.h.in

@@ -15,6 +15,9 @@
 /* "Define if building for EM64T" */
 #cmakedefine ARCH_X86_64
 
+/* Define if AVX-512BW available */
+#cmakedefine HAVE_AVX512
+
 /* internal build, switch on dump support. */
 #cmakedefine DUMP_SUPPORT