[llvm] [AArch64][CodeGen] Fix illegal register aliasing bug for mops instrs (PR #88869)

[Nashe Mncube via llvm-commits]

nasherm wrote:

> Are there any LLVM IR tests that can be added for this? As this is a CodeGen issue we should add these.

Is the `llvm-mc` test not enough? My thinking is that an IR test obfuscates what the actual issue is which shows up much later in the compiler backend

https://github.com/llvm/llvm-project/pull/88869