lib/raid6: Add AVX512 optimized gen_syndrome functions

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 <[email protected]>
Cc: Jim Kukunas <[email protected]>
Cc: Fenghua Yu <[email protected]>
Signed-off-by: Megha Dey <[email protected]>
Signed-off-by: Gayatri Kammela <[email protected]>
Reviewed-by: Fenghua Yu <[email protected]>
Signed-off-by: Shaohua Li <[email protected]>