i82801gx: Support power-on-after-power-fail better

i82801gx: Support power-on-after-power-fail better

Changing CMOS value for power-on-after-power-fail was only honored
after reboot, which is counter intuitive (set from "enable" to "disable",
power-off, replug device -> device turns on; and similar cases).

Change-Id: If1d88c1c34c3333b636ed3ec1e1fb9bea394e615
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/444
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>