[llvm] [AArch64] Fold vector shifts guarded against oversized amounts into USHL (PR #207628)

[David Green via llvm-commits]

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

Sorry for the delay, we have been prioritizing out the release. I think this LGTM now. Thanks

https://github.com/llvm/llvm-project/pull/207628