ARM: dts: imx: update #interrupt-cells for gpio nodes

Change the value of #interrupt-cells of gpio nodes from 1 to 2, so that
the gpio irq type can be specified in device tree.  Also update binding
document to make it clear.

Reported-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
diff --git a/arch/arm/boot/dts/imx27.dtsi b/arch/arm/boot/dts/imx27.dtsi
index 386c769..00bae3a 100644
--- a/arch/arm/boot/dts/imx27.dtsi
+++ b/arch/arm/boot/dts/imx27.dtsi
@@ -121,7 +121,7 @@
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
-				#interrupt-cells = <1>;
+				#interrupt-cells = <2>;
 			};
 
 			gpio2: gpio@10015100 {
@@ -131,7 +131,7 @@
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
-				#interrupt-cells = <1>;
+				#interrupt-cells = <2>;
 			};
 
 			gpio3: gpio@10015200 {
@@ -141,7 +141,7 @@
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
-				#interrupt-cells = <1>;
+				#interrupt-cells = <2>;
 			};
 
 			gpio4: gpio@10015300 {
@@ -151,7 +151,7 @@
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
-				#interrupt-cells = <1>;
+				#interrupt-cells = <2>;
 			};
 
 			gpio5: gpio@10015400 {
@@ -161,7 +161,7 @@
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
-				#interrupt-cells = <1>;
+				#interrupt-cells = <2>;
 			};
 
 			gpio6: gpio@10015500 {
@@ -171,7 +171,7 @@
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
-				#interrupt-cells = <1>;
+				#interrupt-cells = <2>;
 			};
 
 			cspi3: cspi@10017000 {