Add the PowerOn (PonKey) button support to detect power on/off events.
Acked-by: NLinus Walleij <linus.walleij@stericsson.com>
Signed-off-by: NSundar R Iyer <sundar.iyer@stericsson.com>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>