[BesTLA] Add u8s8 kernel for AVX512BW

[luoyu-intel]

Type of Change

Add AVX512BW version of u8s8 GEMM and u8s8 GEMV.
Bring Skylake and Cannonlake to our optimized list.

[luoyu-intel]

Mistral-7B on Skylake server CPU:
AVX512F compute_dtype=fp32

model_print_timings: prompt eval time =  6530.54 ms /  1184 tokens (    5.52 ms per token)
model_print_timings:        eval time =   620.60 ms /    15 runs   (   41.37 ms per token)
model_print_timings:       total time =  7167.66 ms
========== eval time log of each prediction ==========
prediction   0, time: 6530.54ms
prediction   1, time: 43.94ms
prediction   2, time: 41.62ms
prediction   3, time: 41.30ms
prediction   4, time: 41.10ms

AVX512BW, compute_dtype=int8:

model_print_timings: prompt eval time =  4492.60 ms /  1184 tokens (    3.79 ms per token)
model_print_timings:        eval time =   614.60 ms /    15 runs   (   40.97 ms per token)
model_print_timings:       total time =  5121.86 ms
========== eval time log of each prediction ==========
prediction   0, time: 4492.60ms
prediction   1, time: 41.53ms
prediction   2, time: 41.03ms
prediction   3, time: 40.90ms
prediction   4, time: 41.01ms

[luoyu-intel]

From bestla_benchmark:
sgemm FLOPs: 2.7T
igemm FLOPs: 4.5T
int4 group=128 igemm FLOPs: 4.2T