ARM: at91/gpio: add irqdomain and DT support

Add "legacy" type of irqdomain to preserve old-style numbering
and allow smooth transition for both DT and non-DT cases.

Original idea and code by Jean-Christophe Plagniol-Villard.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/arch/arm/boot/dts/at91sam9x5.dtsi b/arch/arm/boot/dts/at91sam9x5.dtsi
index e91391f5..bb0c676 100644
--- a/arch/arm/boot/dts/at91sam9x5.dtsi
+++ b/arch/arm/boot/dts/at91sam9x5.dtsi
@@ -94,6 +94,7 @@
 				interrupts = <2 4>;
 				#gpio-cells = <2>;
 				gpio-controller;
+				interrupt-controller;
 			};
 
 			pioB: gpio@fffff600 {
@@ -102,6 +103,7 @@
 				interrupts = <2 4>;
 				#gpio-cells = <2>;
 				gpio-controller;
+				interrupt-controller;
 			};
 
 			pioC: gpio@fffff800 {
@@ -110,6 +112,7 @@
 				interrupts = <3 4>;
 				#gpio-cells = <2>;
 				gpio-controller;
+				interrupt-controller;
 			};
 
 			pioD: gpio@fffffa00 {
@@ -118,6 +121,7 @@
 				interrupts = <3 4>;
 				#gpio-cells = <2>;
 				gpio-controller;
+				interrupt-controller;
 			};
 
 			dbgu: serial@fffff200 {