dt-bindings: gpio: aspeed,sgpio: Specify #interrupt-cells

Squash warnings such as:

    arch/arm/boot/dts/aspeed/aspeed-ast2500-evb.dtb: sgpio@1e780200: '#interrupt-cells' does not match any of the regexes: 'pinctrl-[0-9]+'

Also, mark #interrupt-cells as required. The kernel devicetrees already
specified it where compatible nodes were defined, and u-boot pulls in
the kernel devicetrees, so this should have minimal practical impact.

Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240530-dt-warnings-gpio-sgpio-interrupt-cells-v2-2-912cd16e641f@codeconstruct.com.au
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/devicetree/bindings/gpio/aspeed,sgpio.yaml

@@ -46,6 +46,9 @@ properties:
 
   interrupt-controller: true
 
+  '#interrupt-cells':
+    const: 2
+
   clocks:
     maxItems: 1
 
@@ -60,6 +63,7 @@ required:
   - '#gpio-cells'
   - interrupts
   - interrupt-controller
+  - '#interrupt-cells'
   - ngpios
   - clocks
   - bus-frequency
@@ -77,6 +81,7 @@ examples:
         reg = <0x1e780200 0x0100>;
         clocks = <&syscon ASPEED_CLK_APB>;
         interrupt-controller;
+        #interrupt-cells = <2>;
         ngpios = <80>;
         bus-frequency = <12000000>;
     };