i82801gx: Use CMOS variable if available for power-on on power failure

i82801gx: Use CMOS variable if available for power-on on power failure

We used a hard coded value for some reason. Don't do that, but use CMOS
instead.

Change-Id: Ib83aa07a3e55bed075150354a060317ebc9d5ba7
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/443
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>