This switches the ADNP GPIO driver to use the gpiolib
irqchip helpers. Also do some random refactoring to make it
look like most other GPIO drivers.

Cc: Roland Stigge <stigge@antcom.de>
Cc: Lars Poeschel <poeschel@lemonage.de>
Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>