mfd: ab8500-sysctrl: Only reboot into charging mode if battery type is known

When a charger is connected, we usually want AB8500 based systems to
reboot into charging-only mode. However, if the battery type cannot
be identified this would be futile, so we'll just shut the system
down instead.

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>