[llvm] [AArch64][SME] Use `mrs %reg, SVCR` rather than ABI routine with `+sme` (PR #156878)

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

> Is there still any test remaining that covers streaming-compatible -> non-streaming without `+sme`?

Yes, there's at least the aptly named `sme-call-streaming-compatible-to-normal-fn-wihout-sme-attr.ll`

https://github.com/llvm/llvm-project/pull/156878