[RISCV] Fold PseudoVMV_V_V with undef passthru, handling policy#106943

lukel97 merged 2 commits intollvm:mainllvm/llvm-project:mainfrom

lukel97:vector-peephole-foldVMV_V_V-undef-passthrulukel97/llvm-project:vector-peephole-foldVMV_V_V-undef-passthruCopy head branch name to clipboard