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

[Nashe Mncube via llvm-commits]

nasherm wrote:

> I think there should also be some LLVM-Lit tests that check the IR CodeGen. The llvm-mc test checks any assembly which the user inputs into the compiler, but if an ACLE Intrinsic is used this can be checked differently within the tests.
> 
> The tests can be written in a way that the output is check not to be a certain value/register. See #77770 for an example of how a test can ensure early-clobber was being respected within IR and CodeGen.

I've written an IR test and updated the PR 


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