[llvm] [NVPTX] Make i16x2 a native type and add supported vec instructions (PR #65432)

[via llvm-commits]

ThomasRaoux wrote:

> Aha. This reproduces the problem: https://godbolt.org/z/K1c4PqYoP

Thanks for the repro. I'm going to land it again with the fix (https://github.com/llvm/llvm-project/pull/65799/commits/2bd3ce7e092a8afa0718dc6a43d53fa3b180d292)

https://github.com/llvm/llvm-project/pull/65432