[llvm] [AArch64] Utilize `XAR` for certain vector rotates (PR #137629)

[Rajveer Singh Bharadwaj via llvm-commits]

Rajveer100 wrote:

For scalable vectors, which instruction do we want to use among `LDxxx`, `MOVAZxxx`, `MOVPRFXxxx` and many others since `MOVIv2d_ns` (and `MOVIxxx`) is for fixed size vectors?

https://github.com/llvm/llvm-project/pull/137629