[llvm] [NVPTX] support packed f32 instructions for sm_100+ (PR #126337)

[Alex MacLean via llvm-commits]

AlexMaclean wrote:

Looks like we need to add the following:
```
  setTruncStoreAction(MVT::v2f32, MVT::v2f16, Expand);
  setTruncStoreAction(MVT::v2f32, MVT::v2bf16, Expand);
```
Otherwise the fp_round will get folded into the store which we can't handle. 

https://github.com/llvm/llvm-project/pull/126337