[GOLD] PowerPC64 support for sym+addend GOT entries

Pass addends to all the GOT handling functions, plus remove some
extraneous asserts.

	PR 28192
	* powerpc.cc (Output_data_got_powerpc): Add addend parameter to
	all methods creating got entries.
	(Target_powerpc::Scan::local): Pass reloc addend to got handling
	functions, and when creating dynamic got relocations.
	(Target_powerpc::Scan::global): Likewise.
	(Target_powerpc::Relocate::relocate): Likewise.  Remove extraneous
	assertions.

(cherry picked from commit 5cdb4f14)