[llvm] [AMDGPU][ISel] Add more trunc store actions regarding bf16 (PR #90493)

[Stanislav Mekhanoshin via llvm-commits]

https://github.com/rampitec approved this pull request.

LGTM. I would also add a scalar test, just to see a single conversion.

https://github.com/llvm/llvm-project/pull/90493