northbridge/intel/i945/northbridge.c: Use define `TOLUD` instead of hardcoded value

Change-Id: I4739c5544aade105399347d239ba64f5115db397
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/5869
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>