[llvm] [AArch64][SME] Tile slices to lazy-save/restore should be RDSVL. (PR #68403)

[Sander de Smalen via llvm-commits]

sdesmalen-arm wrote:

> Is SVL x SVL not the correct size for ZA?

That's indeed the correct size of ZA, but the number of slices to save/restore is simply SVL (because each slice itself is SVL bytes wide).

https://github.com/llvm/llvm-project/pull/68403