Add elfcore_grok_freebsd_note to parse FreeBSD ELF core notes.

Add elfcore_grok_freebsd_note to parse FreeBSD ELF core notes.

Move parsing of FreeBSD-specific ELF core notes out of elfcore_grok_note
into a new elfcore_grok_freebsd_note function.  Add core note grok routines
for FreeBSD's psinfo and prstatus notes while here rather than depending
on the native handling in elfcore_grok_note.

bfd/ChangeLog:

	* elf.c (elfcore_grok_note): Remove handling of NT_X86_XSTATE for
	FreeBSD.  Remove case for NT_FREEBSD_THRMISC.
	(elfcore_grok_freebsd_psinfo): New function.
	(elfcore_grok_freebsd_prstatus): New function.
	(elfcore_grok_freebsd_note): New function.
	(elf_parse_notes): Use "elfcore_grok_freebsd_note" for "FreeBSD"
	notes.