[llvm] [RISCV][TTI] Scale the cost of FP-Int conversion with LMUL (PR #87506)

[Luke Lau via llvm-commits]

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lukel97 wrote:

Nit, can this be renamed to `cast-half` since it tests both zvfh and zvfhmin?

https://github.com/llvm/llvm-project/pull/87506