find libnvToolsExt instead of using only hardcoded path (#16714)

find libnvToolsExt instead of using only hardcoded path (#16714)

Summary:
This changes the libnvToolsExt dependency to go through CMake find_library.

I have a machine where cuda libs, and libnvToolsExt in particular, are in the "usual library locations". It would be neat if we could find libnvToolsExt and use the path currently hardcoded as default.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16714

Differential Revision: D14020315

Pulled By: ezyang

fbshipit-source-id: 00be27be10b1863ca92fd585f273d50bded850f8