[PowerPC] hoist xxspltib out of loop body (#127121)
Fixes https://github.com/llvm/llvm-project/issues/127119
Remove `hasSideEffects` from `xxspltib` since there is no special
restriction specified in the ISA that prevent it from being reordered,
move, CSE, or LICM. Removing this restriction will allow `xxspltib` to
be hoisted out of loop bodies.
