[llvm] [RISCV][TTI] Support fdiv/udiv/sdiv/srem/urem in getArithmeticInstrCost (PR #89170)

[Luke Lau via llvm-commits]

lukel97 wrote:

> What's the history of why the cost model tests use `-riscv-v-fixed-length-vector-lmul-max=1`? That prevents fixed vector tests from covering LMULs larger than 1.

First commit adding vector cost model tests I can find is https://reviews.llvm.org/D99142, presumably back when fixed vector support was new

https://github.com/llvm/llvm-project/pull/89170