[llvm] [PowerPC] Replace vspltisw+vadduwm instructions with xxleqv+vsubuwm for adding the vector {1, 1, 1, 1} (PR #160882)

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Himadhith wrote:

> I'm guessing this is not ready to be reviewed as it need https://github.com/llvm/llvm-project/pull/160476/files to be in first enable to show the difference.

Yes as soon as the NFC patch gets merged I will rebase and the file should reflect the changes. Should I keep this as a draft till then?

https://github.com/llvm/llvm-project/pull/160882