[llvm] [LV] Trim VFs that cause vector splitting when tail-folding with EVL (PR #222836)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

I don't think this should be the responsibility of VPlan, I think the RISC-V getCastInstrCost change in TTI is a better place to do it. Can we go with that PR instead?

Since IIUC the only time we'll end up with a type that needs split is when there's casts involved. 

https://github.com/llvm/llvm-project/pull/222836