Create dwarf2/section.[ch]

Create dwarf2/section.[ch]

This moves some section-handling code from dwarf2read.c into new
files, dwarf2/section.[ch].

gdb/ChangeLog
2020-02-08  Tom Tromey  <tom@tromey.com>

	* dwarf2read.h (struct dwarf2_section_info, dwarf2_read_section):
	Move to dwarf2/section.h.
	* dwarf2read.c (get_containing_section, get_section_bfd_owner)
	(get_section_bfd_section, get_section_name)
	(get_section_file_name, get_section_id, get_section_flags)
	(dwarf2_section_empty_p, dwarf2_read_section): Moe to
	dwarf2/section.c.
	* dwarf2/section.h: New file.
	* dwarf2/section.c: New file, from dwarf2read.c.
	* Makefile.in (COMMON_SFILES): Add dwarf2/section.c.

Change-Id: I9f8498094cf99d9521e9481622ce8adbd453daf4