Move graph util to fx2trt (#64064)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64064
Move original util in torch2trt to fx2trt dir since torch2trt is gonne be deprecated. This is a follow up diff for D30379124
Test Plan: manual
Reviewed By: yinghai, mikekgfb
Differential Revision: D30591687
fbshipit-source-id: ae0e59dfbc2d2e2aa4f3ccea7cff2291c7deb388
