[llvm] [NVPTX] Add family-specific architectures support (PR #141899)

[Alex MacLean via llvm-commits]

https://github.com/AlexMaclean approved this pull request.

LGTM. While there are still some points I think could be clarified further I think this is a step in the right direction. Please wait for @Artem-B's review prior to landing. 

https://github.com/llvm/llvm-project/pull/141899