[llvm] [PowerPC] xxsplti hoist out of loop (PR #127121)

[Lei Huang via llvm-commits]

https://github.com/lei137 commented:

In general this looks good to me.  However, would be good if you can do a NFC pre-commit of the new test added, so this patch can show the changes.

https://github.com/llvm/llvm-project/pull/127121