[llvm] [InstCombine][RISCV] Convert VPIntrinsics with splat operands to splats (PR #65706)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM! Probably worthwhile getting some other reviewers who've worked with VectorCombine to take a look at it too

We could probably also extend this for unary VP ops in the future?

https://github.com/llvm/llvm-project/pull/65706