bmips: dts: fix warnings

- Add missing interrupt-parent to ext_intc.
- Add missing #address-cells and #size-cells to gpio_cntl.
- Use proper gpio handle for gpios (ar-5315u).

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

target/linux/bmips/dts/bcm6318.dtsi

@@ -103,6 +103,7 @@
 			interrupt-controller;
 			#interrupt-cells = <2>;
 
+			interrupt-parent = <&periph_intc>;
 			interrupts = <BCM6318_IRQ_EXT0>,
 				     <BCM6318_IRQ_EXT1>,
 				     <BCM6318_IRQ_EXT2>,
@@ -143,6 +144,8 @@
 		};
 
 		gpio_cntl: syscon@10000080 {
+			#address-cells = <1>;
+			#size-cells = <1>;
 			compatible = "brcm,bcm6318-gpio-sysctl",
 				     "syscon", "simple-mfd";
 			reg = <0x10000080 0x80>;