[llvm-objdump/llvm-readobj/obj2yaml/yaml2obj] Support DT_PPC_GOT and DT_PPC_OPT

In glibc, DT_PPC_GOT indicates that PowerPC32 Secure PLT ABI is used.
I plan to use it in D62464.

DT_PPC_OPT currently indicates if a TLSDESC inspired TLS optimization is
enabled.

Reviewed By: grimar, jhenderson, rupprecht

Differential Revision: https://reviews.llvm.org/D62851

llvm-svn: 362569