[ELF][PPC64] Rename some PPC64 ELFv2 specific RelExpr from R_PPC_* to R_PPC64_*
The following abstract relocation types (RelExpr) are PPC64 ELFv2 ABI specific,
not used by PPC32. So rename them to prevent confusion when the PPC32 port is improved.
- R_PPC_CALL R_PPC_CALL_PLT: R_PPC_CALL_PLT represents R_PPC64_REL14 and R_PPC64_REL24. If the function is not preemptable, R_PPC_CALL_PLT can be optimized to R_PPC_CALL: the formula adjusts the symbol VA from the global entry point to the local entry point.
- R_PPC_TOC: represents R_PPC64_TOC. We don't have a test. Add one to ppc64-relocs.s Rename it to R_PPC64_TOCBASE because @tocbase is the assembly form.
Reviewed By: ruiu
Differential Revision: https://reviews.llvm.org/D62800