Optimize erratum 843419 fix.

Optimize erratum 843419 fix.

gold/ChangeLog:
	* aarch64.cc (AArch64_insn_utilities::is_adr): New method.
	(AArch64_insn_utilities::aarch64_adr_encode_imm): New method.
	(AArch64_insn_utilities::aarch64_adrp_decode_imm): New method.
	(E843419_stub): New sub-class of Erratum_stub.
	(AArch64_relobj::try_fix_erratum_843419_optimized): New method.
	(AArch64_relobj::section_needs_reloc_stub_scanning): Try optimized fix.
	(AArch64_relobj::create_erratum_stub): Add 1 argument.
	(Target_aarch64::scan_erratum_843419_span): Pass in adrp insn offset.