[PowerPC] Use assembler source in MC tests

A couple of old test cases in test/MC/PowerPC were still using
LLVM IR.  Now that we have a working assembler, we can move
them to assembler tests instead:
  ppc64-initial-cfa.ll
  ppc64-relocs-01.ll
  ppc64-tls-relocs-01.ll




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183829 91177308-0d34-0410-b5e6-96231b3b80d8