[llvm] [RISCV][TTI] Add cost model for ROTL/ROTR (PR #170824)

[Sudharsan Veeravalli via llvm-commits]

svs-quic wrote:

> LGTM too. We should also probably handle vectors with vrol/vror when there's Zvkb

Will address this in a follow up.

https://github.com/llvm/llvm-project/pull/170824