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

[Tony Varghese via llvm-commits]

https://github.com/tonykuttai requested changes to this pull request.

Please modify the `description` to reflect that 
- `ADD` operation substituted with `SUB`
- `Build vector of all 1s` in RHS getting replaced with `Build vector of all -1s`

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