Share the code to format "info proc mappings" entries for FreeBSD.

Share the code to format "info proc mappings" entries for FreeBSD.

gdb/ChangeLog:

	* fbsd-nat.c (fbsd_nat_target::info_proc) Use
	fbsd_info_proc_mappings_header and fbsd_info_proc_mappings_entry.
	* fbsd-tdep.c (fbsd_vm_map_entry_flags): Mark static.
	(fbsd_info_proc_mappings_header, fbsd_info_proc_mappings_entry):
	New functions.
	(fbsd_core_info_proc_mappings): Use fbsd_info_proc_mappings_header
	and fbsd_info_proc_mappings_header.
	* fbsd-tdep.h (fbsd_vm_map_entry_flags): Remove.
	(fbsd_info_proc_mappings_header, fbsd_info_proc_mappings_entry):
	New.