[llvm] [NVPTX] Generalize and extend upsizing when lowering 8/16-bit-element vector loads/stores (PR #119622)

[Drew Kersnar via llvm-commits]

dakersnar wrote:

I'm seeing evidence that `Isv2x16VT(VT) || VT == MVT::v4i8` is already being checked at quite a few places. We may want to generalize the helper function `isVectorElementTypeUpsized` helper I just created and use it everywhere. Name suggestions appreciated.

https://github.com/llvm/llvm-project/pull/119622