This adds support for the power-on buttons of MC13783 PMIC.

Signed-off-by: Philippe Rétornaz <philippe.retornaz@epfl.ch>
Acked-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>