[llvm] [PowerPC][AIX] Emit PowerPC version for XCOFF (PR #95510)

[via llvm-commits]

EsmeYi wrote:

Addressed parts of comments.
Will update after #97541 merged, where the function `getNormalizedPPCTuneCPU()` can be called in [llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp](https://github.com/llvm/llvm-project/pull/95510/files/2349e17222665555c918e5a13b4d15347ce3ba79#diff-17b326b45ef392288420bed274616afa7df81b27576c96723b3c25f5198dc398) and the `XCOFF::getCpuID()` will be updated then.

https://github.com/llvm/llvm-project/pull/95510