gpio: pca953x: use gpiolib irqchip helpers

This switches the PCA953x driver over to using the gpiolib irqchip
helpers to handle the threaded interrups cascaded off this
GPIO chip.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -519,6 +519,7 @@ config GPIO_PCA953X
 config GPIO_PCA953X_IRQ
 	bool "Interrupt controller support for PCA953x"
 	depends on GPIO_PCA953X=y
+	select GPIOLIB_IRQCHIP
 	help
 	  Say yes here to enable the pca953x to be used as an interrupt
 	  controller. It requires the driver to be built in the kernel.