[llvm] AMDGPU: Legalize atomicrmw fadd for v2f16/v2bf16 for local memory (PR #95393)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Jun 15, 3:51 AM EDT**: @arsenm started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/95393).


https://github.com/llvm/llvm-project/pull/95393