[llvm] [RISCV] Add tune info for mem* expansion (PR #118439)

[Alex Bradbury via llvm-commits]

asb wrote:

> > What's your plan for the getters in TargetLowering for the same properties? These are queried elsewhere in the codebase.
> 
> I don't get what you mean, these getters should return the same values that we set in XXXTargetLowering?

Sorry, I'd somehow missed the part that assigned the underlying values used by those getters in RISCVISelLowering. All good.

https://github.com/llvm/llvm-project/pull/118439