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

[Dmitri Gribenko via llvm-commits]

gribozavr wrote:

> Can we fix it forward? I'll prepare a patch.

The HEAD has been broken for more than a day, and we need to get to green ASAP. I pushed the revert.

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