[gold][aarch64] Fix erratum 835769.

[gold][aarch64] Fix erratum 835769.

gold/ChangeLog:

	* aarch64.cc (AArch64_insn_utilities::BYTES_PER_INSN): Move
	defintion outside class definition.
	(AArch64_insn_utilities::AARCH64_ZR): New static constant.
	(AArch64_insn_utilities::aarch64_op31): New member.
	(AArch64_insn_utilities::aarch64_ra): New member.
	(AArch64_insn_utilities::aarch64_mac): New member.
	(AArch64_insn_utilities::aarch64_mlxl): New member.
	(ST_E_835769): New global enum member.
	(Stub_table::relocate_stubs): Add 835769 handler.
	(Stub_template_repertoire::Stub_template_repertoire): Install new
	stub type.
	(AArch64_relobj::scan_errata): This func is renamed from
	scan_erratum_843419.
	(AArch64_relobj::do_count_local_symbols): Add 835769 handler.
	(AArch64_relobj::do_relocate_sections): Add 835769 handler.
	(AArch64_relobj::scan_sections_for_stubs): Add 835769 handler.
	(Target_aarch64::scan_erratum_835769_span): New method.
	(Target_aarch64::create_erratum_stub): New method.
	(Target_aarch64::is_erratum_835769_sequence): New method.
	(Target_aarch64::scan_erratum_843419_sequence): Move part of the
	code into create_erratum_stub.
	* options.h (fix_cortex_a53_835769): New option.