[llvm] AMDGPU: Allow operand folding between loop body and its preheader (PR #137022)

[Akash Dutta via llvm-commits]

akadutta wrote:

This is a temporary change to fix an issue. These changes should go away once [#128687](https://github.com/llvm/llvm-project/pull/128687) and [#116953 ](https://github.com/llvm/llvm-project/pull/116953) land.

https://github.com/llvm/llvm-project/pull/137022