[llvm] [MachineCopyPropagation][NFC] Refactor EliminateSpillageCopies (PR #192609)

[Jack Styles via llvm-commits]

Stylie777 wrote:

I am investigating the RegMask issues on PowerPC, my builds don't target this locally so I missed this before upstreaming.

https://github.com/llvm/llvm-project/pull/192609