[llvm] [AArch64] Merge scaled and unscaled narrow zero stores (PR #136705)

[Guy David via llvm-commits]

guy-david wrote:

With recent LLVM, I no longer see any cases of this happening on a very large bitcode repository, so it's possible ISel combines the stores and nothing in the codegen creates this pattern. Nonetheless, I think it's good to have it.

https://github.com/llvm/llvm-project/pull/136705