lib/raid6: Add AVX512 optimized gen_syndrome functions

Optimize RAID6 gen_syndrom functions to take advantage of
the 512-bit ZMM integer instructions introduced in AVX512.

AVX512 optimized gen_syndrom functions, which is simply based
on avx2.c written by Yuanhan Liu and sse2.c written by hpa.

The patch was tested and benchmarked before submission on
a hardware that has AVX512 flags to support such instructions

Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jim Kukunas <james.t.kukunas@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Megha Dey <megha.dey@linux.intel.com>
Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>

lib/raid6/algos.c

@@ -49,6 +49,10 @@ const struct raid6_calls * const raid6_algos[] = {
 	&raid6_avx2x1,
 	&raid6_avx2x2,
 #endif
+#ifdef CONFIG_AS_AVX512
+	&raid6_avx512x1,
+	&raid6_avx512x2,
+#endif
 #endif
 #if defined(__x86_64__) && !defined(__arch_um__)
 	&raid6_sse2x1,
@@ -59,6 +63,11 @@ const struct raid6_calls * const raid6_algos[] = {
 	&raid6_avx2x2,
 	&raid6_avx2x4,
 #endif
+#ifdef CONFIG_AS_AVX512
+	&raid6_avx512x1,
+	&raid6_avx512x2,
+	&raid6_avx512x4,
+#endif
 #endif
 #ifdef CONFIG_ALTIVEC
 	&raid6_altivec1,