[llvm] [RISCV] Expand vp.stride.load to splat of a scalar load. (PR #98140)

[Yeting Kuo via llvm-commits]

yetingk wrote:

@topperc and @lukel97 Do you have a plan to implement vp.splat? I could go to implement it if you don't have a a plan of it.

https://github.com/llvm/llvm-project/pull/98140