[NFC][PowerPC] Lockdown instructions of vspltisw for addition of vector of 1s#160476

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

Himadhith:himadhith/NFC_vector_all_onesHimadhith/llvm-project:himadhith/NFC_vector_all_onesCopy head branch name to clipboard