Enable GPTQ in executorch (#2425)

Summary:
Previously we just added the code but didn't test it, this PR also tests gptq locally to make sure we can produce a model using gptq from torchao repo

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Pull Request resolved: https://github.com/pytorch/executorch/pull/2425

Test Plan: python3 -m examples.models.llama2.export_llama -c stories110M.pt -p params.json -qmode 8da4w-gptq -X -d fp32

Reviewed By: manuelcandales

Differential Revision: D54922375

Pulled By: jerryzh168

fbshipit-source-id: a77e44e0d5efa0e070cc32f54d784ba5c8a23c7f