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>