PowerPC64 xlate_pcrel_opt

PowerPC64 xlate_pcrel_opt

We can easily support an offset on the second instruction of a
sequence marked with R_PPC64_PCREL_OPT.  For example,
  pla ra,symbol@pcrel
  ld rt,off(ra)
can be optimised to
  pld rt,symbol+off@pcrel
  nop

	* elf64-ppc.c (xlate_pcrel_opt): Add poff parameter.  Allow offset
	on second insn, return it in poff.
	(ppc64_elf_relocate_section): Add offset to paddi addend for
	PCREL_OPT.