gpio: etraxfs: add interrupt support

On ETRAX FS, all pins on the first port (and only the first port) have
interrupt support.

On ARTPEC-3, all pins on all ports have interrupt support.  However,
there are only eight interrupts.  Each of the interrupts is associated
with a group of pins and for each interrupt the one pin from the group
which will trigger it can be selected.

Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 3a9dc1a..37d9418 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -171,6 +171,7 @@
 	depends on CRIS || COMPILE_TEST
 	depends on OF
 	select GPIO_GENERIC
+	select GPIOLIB_IRQCHIP
 	help
 	  Say yes here to support the GPIO controller on Axis ETRAX FS SoCs.