[RISCV] Move performCombineVMergeAndVOps into RISCVFoldMasks#71764

lukel97 wants to merge 6 commits intollvm:mainllvm/llvm-project:mainfrom

lukel97:fold-mask/vmerge-into-opslukel97/llvm-project:fold-mask/vmerge-into-opsCopy head branch name to clipboard