arm64: dts: apm: add required gpio-cells to DW APB GPIO controller port

The Synopsys DesignWare APB GPIO controller port must have gpio-cells
property, as pointed by dtschema:

arch/arm64/boot/dts/apm/apm-mustang.dt.yaml: gpio@1c024000: gpio-controller@0: '#gpio-cells' is a required property

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Olof Johansson <[e-mail]>

arch/arm64/boot/dts/apm/apm-shadowcat.dtsi

···
 			porta: gpio-controller@0 {
 				compatible = "snps,dw-apb-gpio-port";
 				gpio-controller;
+				#gpio-cells = <2>;
 				snps,nr-gpios = <32>;
 				reg = <0>;
 			};

arch/arm64/boot/dts/apm/apm-storm.dtsi

···
 			porta: gpio-controller@0 {
 				compatible = "snps,dw-apb-gpio-port";
 				gpio-controller;
+				#gpio-cells = <2>;
 				snps,nr-gpios = <32>;
 				reg = <0>;
 			};