iopsys-brcm63xx-arm: smarthub3: Define action for WPS button

This will make the button "work", i.e. it was working before, just no
action was defined.

iopsys-brcm63xx-arm/smarthub3/base-files/etc/config/buttons

+
+config button WPS
+	list button gpio_wps
+	option hotplug wpsbutton
+	option enable 1