[llvm] [RISCV][CostModel] Updates reduction and shuffle cost (PR #77342)

[Philip Reames via llvm-commits]

preames wrote:

After https://github.com/llvm/llvm-project/pull/79402 lands, I think all the pieces of this have gone in right?  If not, can you rebase so what's left is visible?

https://github.com/llvm/llvm-project/pull/77342