Remove spurious AVX512 requirement and add AVX2/FMA3 guard
-/* need a new enough GCC for avx512 support */
-#if (( defined(__GNUC__) && __GNUC__ > 6 && defined(__AVX512CD__)) || (defined(__clang__) && __clang_major__ >= 9))
+#if defined(HAVE_FMA3) && defined(HAVE_AVX2)
#define HAVE_SROT_KERNEL 1
