Revert " [PowerPC] frontend get target feature from backend with cpu name (#137670)"
This reverts commit 9208b343e962b9f1140ee345c0050a3920bdcbf2.
TargetParser shouldn't re-run the PPC subtarget tablegen target, it
should define its own `-gen-ppc-target-def` rule like all the other
targets do in llvm/include/llvm/TargetParser/CMakeLists.txt .
One user reported that there are incorrect CMake dependencies after this
change, so I will roll this back in the meantime.