ARM: dts: am335x: lxm: fix PCA9539 GPIO expander properties

The PCA9539 GPIO expander requires GPIO controller properties to operate
properly.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Acked-by: Tony Lindgren <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>

arch/arm/boot/dts/am335x-lxm.dts

···
 	serial_config1: serial_config1@20 {
 		compatible = "nxp,pca9539";
 		reg = <0x20>;
+		gpio-controller;
+		#gpio-cells = <2>;
 	};
 
 	serial_config2: serial_config2@21 {
 		compatible = "nxp,pca9539";
 		reg = <0x21>;
+		gpio-controller;
+		#gpio-cells = <2>;
 	};
 
 	tps: tps@2d {