[obj2yaml] - Support PPC64 relocation types.
We do not support them and fail with llvm_unreachable currently.
This is not the only target we do not support and also seems we are missing
the tests for those we have already. But I needed this one for another patch,
so posted it separatelly.
Relocation names are taken from llvm\include\llvm\BinaryFormat\ELFRelocs\PowerPC64.def
Differential revision: https://reviews.llvm.org/D67615
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@372109 91177308-0d34-0410-b5e6-96231b3b80d8