[llvm] [RISCV] Add TuneJumpIsExpensive (PR #191374)

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> What is the advantage of a tuning flag given that we already have `-mllvm -jump-is-expensive`?
> 
> Could we put it in `RISCVTuneInfo` if we want to enable it on a specific CPU?

No difference I think. I can change it to a field in RISCVTuneInfo.

https://github.com/llvm/llvm-project/pull/191374