Adding elu,selu,softsign support for fx2trt (#70811)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70811
Add support of the above ops in fx2trt.
Reviewed By: 842974287
Differential Revision: D33407911
fbshipit-source-id: 8c635ddbd1cae6b0a0a04d345b0e0347111a6619
