[llvm] [AArch64][SVE] Pair SVE fill/spill into LDP/STP with -msve-vector-bits=128. (PR #134068)

[Paul Walker via llvm-commits]

https://github.com/paulwalker-arm approved this pull request.

Thanks @rj-jesus for this and the previous foundation work.  To my eye I think we've landed on a clean solution so let's see what the buildbots think of it :)

https://github.com/llvm/llvm-project/pull/134068