[llvm] [NVPTX][NFC] Refactor and cleanup NVPTXISelLowering call lowering 2/n (PR #137666)

[Artem Belevich via llvm-commits]

https://github.com/Artem-B requested changes to this pull request.

Hold on a sec with merging. I've missed all the changes in NVPTXISelLowering.cpp. Thanks to GitHub for hiding the diff.

https://github.com/llvm/llvm-project/pull/137666