[llvm] AMDGPU: Use helper function for use/def chain walk (PR #129052)

[Matt Arsenault via llvm-commits]

arsenm wrote:

ValueTracker. I'd like to rewrite this one to look more like PeepholeOpt in a few ways, but I don't think we can replace one with the other 

https://github.com/llvm/llvm-project/pull/129052