Add precision option (#1361)
Summary:
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1361
Add an option to specify precision (amp, fp32, fp16).
(Note: I added this back in november, and forgot to submit it as a PR. It was used to generate the AMP numbers for DDP / FSDP and PT2)
Test Plan: Imported from OSS
Reviewed By: wconstab
Differential Revision: D42437978
Pulled By: davidberard98
fbshipit-source-id: e026e3ebbf5849563e3a5e1f25d270f47e869afb
