[POWERPC] Correct AC Power: in /proc/pmu/info on ibook1

/proc/pmu/info contains AC Power: 0 when booting without battery.
Force AC Power, it will be updated whenever the battery state changes.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>