Account for padding in FreeBSD/mipsn32 NT_PRSTATUS notes.

Account for padding in FreeBSD/mipsn32 NT_PRSTATUS notes.

Add a new ELF backend method to grok FreeBSD NT_PRSTATUS core dump
notes.  Define a method for MIPS N32 to override the default
elfcore_grok_freebsd_prstatus that accounts for additional padding
between pr_pid and pr_reg that is not present in other 32-bit FreeBSD
platforms.

	* elf-bfd.h (struct elf_backend_data): Add
	`elf_backend_grok_freebsd_prstatus'.
	* elf.c (elfcore_grok_freebsd_note): Call
	`elf_backend_grok_freebsd_prstatus' to handle NT_PRSTATUS if
	present.
	* elfn32-mips.c (elf_n32_mips_grok_freebsd_prstatus): New
	function.
	(elf_backend_grok_freebsd_prstatus): Define.
	* elfxx-target.h (elf_backend_grok_freebsd_prstatus): Define.
	(elfNN_bed): Initialize `elf_backend_grok_freebsd_prstatus'.