[llvm] [RISCV] Emit VP strided loads/stores in RISCVGatherScatterLowering (PR #98111)

[Luke Lau via llvm-commits]

lukel97 wrote:

This patch should be more or less NFC so I don't think it's important to backport it. #100116 might provide some minor optimisations though if people want to see that in LLVM 19

https://github.com/llvm/llvm-project/pull/98111