mfd: ab8500-sysctrl: If a charger is present, reboot instead

If a charger is attached on power off, reboot the system
into charging mode instead of powering it off.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Reviewed-by: Karl KOMIEROWSKI <karl.komierowski@stericsson.com>