[RISCV] Add a new subtarget feature for throttled FP64 vector performance#162399

mshockwave merged 2 commits intollvm:mainllvm/llvm-project:mainfrom

mshockwave:patch/riscv/throttled-fp64-featuremshockwave/llvm-project:patch/riscv/throttled-fp64-featureCopy head branch name to clipboard