[PowerPC][X86] Make cpu id builtins target independent and lower for PPC (#68919)

Make __builtin_cpu_{init|supports|is} target independent and provide an
opt-in query for targets that want to support it. Each target is still
responsible for their specific lowering/code-gen. Also provide code-gen
for PowerPC.

I originally proposed this in https://reviews.llvm.org/D152914

 and this
addresses the comments I received there.

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Co-authored-by: Nemanja Ivanovic <nemanjaivanovic@nemanjas-air.kpn>
Co-authored-by: Nemanja Ivanovic <nemanja@synopsys.com>