[Kernel] Pass a device pointer into the quantize kernel for the scales

[tlrmchlsmth]

This PR changes the int8 static quantize kernel so it takes a torch::Tensor instead of a float for the scale. This lets us keep it on the device in order to avoid calling item on the tensor, which causes a synchronization between the CPU and GPU and breaks CUDA graphs.

With this PR plus #5137, vllm can run nm-testing/tinyllama-one-shot-static-quant-test-compressed with enforce_eager=False

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[varun-sundar-rabindranath]

LGTM 👍

[dsikka]

LGTM given tests pass

[mgoin]

Nice fix!

[pcmoritz]

Thanks for fixing -- this also makes the handling of the int8 scales the same as the fp8 scales which is nice :)