mfd: da9062: add support for the DA9062 GPIOs in the core

Currently the da9062 GPIO's aren't available. The patch adds the support
to make these available by adding a gpio device with the corresponding
irq resources. Furthermore the patch fixes a minor style issue for the
onkey device.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>