[PPC][PPC64] PPC_REL14 and PPC64_REL14 relocations

When linking the linux kernel on ppc64 and ppc
ld.lld: error: unrecognized reloc 11
11 is PPC_REL14 and PPC64_REL14

Differential revision: https://reviews.llvm.org/D54868

llvm-svn: 348255