[llvm] [AArch64][SVE] Use multi-vector spill/fill instructions in pseudo expansion (PR #187396)

[Amara Emerson via llvm-commits]

aemerson wrote:

> Sorry, I forgot about this PR. The changes generally make sense to me, but still left some comments.

No this was still on me to remove the existing support (it was more involved than expected so I shelved it). Do you still want me to do that?

https://github.com/llvm/llvm-project/pull/187396