[llvm] [ARM] Replace redundant cmpz transforms in tablegen with ISelLowering (NFCI) (PR #193557)

[via llvm-commits]

AZero13 wrote:

@arsenm I understand that this may be a bit of bandwidth on your end. Nevertheless, I believe this is worth it because unifying this here because the special cases of cmpz-cmn in tablegen really serve no benefit over this.

https://github.com/llvm/llvm-project/pull/193557