[Kernel] Vectorized FP8 quantize kernel

[comaniac]

Inspired by #5146, this PR improves FP8 quantize kernel by vectorizing data transfer to better utilize memory bandwidth. Microbenchmark shows that this improved kernel can achieve 1.0x-1.5x speedup (especially when hidden size is large).

In details, we applied 3 optimizations:

1. Use inverted scale so that most divisions are changed to multiplications.
2. Unroll the loop by 4 times to improve ILP.
3. Use vectorized 4 to transfer data between HBM and SRAM.

cc @pcmoritz @robertgshaw2-neuralmagic

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[tlrmchlsmth]

Could you make sure there's a unit test, especially for the case where num_elems %4 != 0?

[comaniac]

Could you make sure there's a unit test, especially for the case where num_elems %4 != 0?

Thanks for the suggestion. Will do.

[tlrmchlsmth]

thanks for adding the tests!

[pcmoritz]

Thanks for improving this kernel :)