[llvm] [AArch64][SVE] Use ADD/ADR instead of MUL/MLA for x*N (PR #198566)

[Paul Walker via llvm-commits]

https://github.com/paulwalker-arm commented:

FYI: Typically for work like this we'd have the new tests as the first commit on the PR with the code changes in later commits.  Doing this makes it very easy to see the affect of the code changes.

https://github.com/llvm/llvm-project/pull/198566