After finding the missing bit poweroff works now.

I cleaned up the patch and moved most of the dsdt.dsl and
acpi_tables.c into the southbrige/northbridge directory.
Updated patch should fix abuild error and incorporates suggestions
on irc by uwe (thanks for the comments).
Thanks to Idwer Vollering <vidwer@gmail.com> for the original patch.

Tested:
  Linux (poweroff, powerbutton event)
  XP (poweroff, powerbutton event)

Abuild-tested

Signed-off-by: Tobias Diedrich <ranma+coreboot@tdiedrich.de>
Acked-by: Stefan Reinauer <stepan@coreboot.org>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@6127 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1