[llvm] [RISCV][CostModel] add cost for cttz/ctlz under the non-zvbb (PR #117515)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

Do we still want to be using the intrinsic cost table for vector instructions? IIUC this was added before we started taking into account LMUL costs. Should we be migrating away from this eventually? cc @preames 

https://github.com/llvm/llvm-project/pull/117515