Type Promote Div (#4516)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/4516

In decomposition of Hardsigmoid, we see a divide by 6. When we lift this scalar to a tensor, we then see that the divisor is int64, and the dividend is float32. This allows us to remove the Mixed Dtype and also helps us delegate to XNNPACK

Reviewed By: tarun292, digantdesai

Differential Revision: D60492342

fbshipit-source-id: be059eee4481fcae7683a99468993d80d0f8d50a