[fx2trt] More controls over output dtypes (#65959)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65959
Give some more controls over the output dtype of a trt engine. Previously it would be fp16 if we turn on fp16_mode. This diff allows the engine to generate fp32 output with fp16_mode=True.
Test Plan: CI
Reviewed By: kflu, wushirong
Differential Revision: D31243929
fbshipit-source-id: 09c752e6f382d6ad169da66878d9a9277c134869
