[llvm] [AArch64][SME] Introduce CHECK_MATCHING_VL pseudo for streaming transitions (PR #157510)

[Benjamin Maxwell via llvm-commits]

https://github.com/MacDue approved this pull request.

I have a few minor comments on tests/comments, but the main PR LGTM :+1: 

https://github.com/llvm/llvm-project/pull/157510