[llvm] [PowerPC] Prefer VSX compare in vector selection (PR #65295)

[Qiu Chaofan via llvm-commits]

ecnelises wrote:

This is splitted from https://reviews.llvm.org/D75895. Since VSX instructions can use twice registers than VMX, it does no harm to codegen.

https://github.com/llvm/llvm-project/pull/65295