[llvm] [NVPTX] Optimize v2x16 BUILD_VECTORs to PRMT (PR #116675)

[Justin Fargnoli via llvm-commits]

justinfargnoli wrote:

> @[justinfargnoli](https://github.com/justinfargnoli) requested a review from [Artem-B](https://github.com/Artem-B) 

Apologies, I didn't mean to click the request review button. 

https://github.com/llvm/llvm-project/pull/116675