gpio: adnp: switch to use irqchip helpers

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: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 1fe93eb..ec27ec0 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -690,6 +690,7 @@
 config GPIO_ADNP
 	tristate "Avionic Design N-bit GPIO expander"
 	depends on I2C && OF_GPIO
+	select GPIOLIB_IRQCHIP
 	help
 	  This option enables support for N GPIOs found on Avionic Design
 	  I2C GPIO expanders. The register space will be extended by powers