binfmt_elf_fdpic: wire up AT_EXECFD, AT_EXECFN, AT_SECURE

These auxvec entries are the only ones left unhandled out of the current
base implementation. This syncs up binfmt_elf_fdpic with linux/auxvec.h
and current binfmt_elf.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>