ARM: dts: keystone: Add missing unit name to interrupt controller

Add base address for GIC as unit address. This also squashes the
following warnings when built with W=1:
arch/arm/boot/dts/keystone-k2hk-evm.dtb: Warning (unit_address_vs_reg): Node /interrupt-controller has a reg or ranges property, but no unit name
arch/arm/boot/dts/keystone-k2l-evm.dtb: Warning (unit_address_vs_reg): Node /interrupt-controller has a reg or ranges property, but no unit name
arch/arm/boot/dts/keystone-k2e-evm.dtb: Warning (unit_address_vs_reg): Node /interrupt-controller has a reg or ranges property, but no unit name

Reported-by: Rob Herring <[e-mail]>
Signed-off-by: Nishanth Menon <[e-mail]>
Signed-off-by: Santosh Shilimkar <[e-mail]>

arch/arm/boot/dts/keystone.dtsi

···
 		reg = <0x00000000 0x80000000 0x00000000 0x40000000>;
 	};
 
-	gic: interrupt-controller {
+	gic: interrupt-controller@2561000 {
 		compatible = "arm,gic-400", "arm,cortex-a15-gic";
 		#interrupt-cells = <3>;
 		interrupt-controller;