[llvm] [TTI][RISCV] Add cost modelling for intrinsic vp.load.ff (PR #160470)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

Generally looks good, it's a shame we have to add so much boilerplate to return the cost of just one intrinsic. But I think it's best to keep things consistent with the other memory intrinsics, i.e. have a dedicated TTI hook for the cost and a dedicated TLI for legality.

https://github.com/llvm/llvm-project/pull/160470