add `OpInfo` for `torch.nn.functional.softplus` (#62317)
Summary:
Addresses facebookresearch/functorch#78.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62317
Reviewed By: malfet
Differential Revision: D30013322
Pulled By: zou3519
fbshipit-source-id: e80affd10b81534234694c9e4326cc68c7efc7fe
