pm2301-charger: Wake system when ext charger is plugged-in

When in suspend state, upon plug-in of external AC charger the
device needs to wake-up and charging operation started.

Signed-off-by: Rupesh Kumar <rupesh.kumar@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Philippe LANGLAIS <philippe.langlais@stericsson.com>