Add sse4/avx2 support for fast x86 int8 (vpmaddubsw/vpmaddwd/vpaddd)

[elvin-n]

• Extend the list of different target for x86 topi
• Extend tests for conv2d x86 int8 for fast i8 x86 platforms

this change in theory can give up to 2x speedup on int8 models vs fp32 models, currently slightly less

Resnet50 performance:

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	Core i7-1185G7 sse4	Core i7-1185G7 avx2	Core i7-1185G7 avx512	Core i7-1185G7 VNNI	Core i7-8700B	Core i5-9400T
	FPS	FPS	FPS	FPS	FPS	FPS
TVM FP32		53	53	53	54	48
TVM int32		12			16
TVM int8 default	34	61	92	142	78	62
TVM int8 atvm		70		134	95	79

[jcf94]

Thanks for your answer! @elvin-n

[elvin-n]

The change in get_fp32_len affected ARM flow - now it started to block by 4 instead previous default 8. It must not affect from performance point of view since NEON SIMD vector size is 64 or 128 bit, but will affect the knowledge database of tuned kernels.

Will verify the performance aspect on ARM. As for backward compatibility - still open question. So far I have an impression that we do not care about it so much.

[elvin-n]

I verified ARM flow and confirm that it started to use 4 channel values instead of 8 for blocking and this fact did not affect performance anyhow (as i expected)