Change section_is_p to a method on dwarf2_section_names

Change section_is_p to a method on dwarf2_section_names

This replaces section_is_p with a method on dwarf2_section_names.

gdb/ChangeLog
2021-03-06  Tom Tromey  <tom@tromey.com>

	* dwarf2/sect-names.h (struct dwarf2_section_names) <matches>: New
	method.
	* dwarf2/read.c (section_is_p): Remove.
	(dwarf2_per_bfd::locate_sections)
	(dwarf2_per_bfd::locate_sections, locate_dwz_sections)
	(locate_v1_virtual_dwo_sections, dwarf2_locate_dwo_sections)
	(dwarf2_locate_common_dwp_sections)
	(dwarf2_locate_v2_dwp_sections, dwarf2_locate_v5_dwp_sections):
	Update.