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

[via llvm-commits]

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ThomasRaoux wrote:

It is linked as making v2i16 a legal type makes the vectorization pass apply vectorization to this IR. I'm not sure why we needed those negative tests in a first place but I don't see a way to separate this out

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