[llvm] [RISCV] Cost ordered bf16/f16 w/ zvfhmin reductions as invalid (PR #114250)

[Luke Lau via llvm-commits]

lukel97 wrote:

Rebased on https://github.com/llvm/llvm-project/pull/114180 and sunk into the FADD case.

https://github.com/llvm/llvm-project/pull/114250