Load debug section only when dumping debug sections

Don't load debug sections if we aren't dumping any debug sections.

	PR binutils/28843
	* objdump.c (dump_any_debugging): New.
	(load_debug_section): Return false if dump_any_debugging isn't
	set.
	(main): Set dump_any_debugging when dumping any debug sections.
	* readelf (dump_any_debugging): New.
	(parse_args): Set dump_any_debugging when dumping any debug
	sections.
	(load_debug_section): Return false if dump_any_debugging isn't
	set.