[llvm] [NVPTX] Add support for f16 fabs (PR #116107)

[Justin Fargnoli via llvm-commits]

justinfargnoli wrote:

Feel free to ignore [comment](https://github.com/llvm/llvm-project/pull/116107#discussion_r1841203171) and [comment](https://github.com/llvm/llvm-project/pull/116107#discussion_r1841210789). I'll file issues for them. 

https://github.com/llvm/llvm-project/pull/116107