[PowerPC] Add some missing PPC64 relocs

All R_PPC_... relocs should also be present (using the same number)
under the corresponding R_PPC64_... name.   The latter were missing
for a couple of cases, which this patch adds.

This is not a big problem when emitting the reloc, because we can
just use the R_PPC_... define instead.  But it is a problem when
*dumping* relocations e.g. using llvm-readobj, because this will
expect only R_PPC64_... values when inspecting a ppc64 ELF file.

llvm-svn: 181451