[llvm] [AArch64] Extend usage of `XAR` instruction for fixed-length operations (PR #139460)

[David Green via llvm-commits]

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

LGTM if the type of the MOVIv2d_ns is changed to v2i64. Thanks

https://github.com/llvm/llvm-project/pull/139460