Refactor amd64 startup SMAP parsing

Extracted from the projects/uefi branch, this change is a reasonable
cleanup and will reduce the diffs to review when bringing in the
UEFI work.

Reviewed by:	kib@
Sponsored by:	The FreeBSD Foundation
Sync with NetBSD.  The funtional change is to make the output when
comparing a directory to an mtree file more compatible with fmtree when
FreeBSD 9 compatiblity mode is on.  This output is clearly intended for
humans not computers, but some tools such as mergemaster's -U option rely
on it.

MFC after:	3 days
Fix reference to ioctl(2).
f_die() (see `bsdconfig includes -dF die') uses a dialog box (and has been
documented as such; I just forgot). These utilities are command-line only
and as such should stick to either using f_die without arguments or printf)
mdoc: remove EOL whitespace.