Change two more functions to be methods on die_info

Change two more functions to be methods on die_info

This changes lookup_addr_base and lookup_ranges_base to be methods on
die_info.

gdb/ChangeLog
2020-03-26  Tom Tromey  <tom@tromey.com>

	* dwarf2/die.h (struct die_info) <addr_base, ranges_base>: New
	methods.
	* dwarf2/read.c (lookup_addr_base): Move to die.h.
	(lookup_ranges_base): Likewise.
	(read_cutu_die_from_dwo, read_full_die_1): Update.