ARM: dts: dh-imx6: add u-boot specific wdt-reboot node

The wdt-reboot node is needed for the sysreset_watchdog driver to
register a watchdog as a reset handler in case 'CONFIG_SYSRESET' is
enabled.
Signed-off-by: NClaudius Heine <ch@denx.de>

arch/arm/dts/imx6q-dhcom-pdk2-u-boot.dtsi

+// SPDX-License-Identifier: (GPL-2.0+)
+/*
+ * Copyright (C) 2019 Claudius Heine <ch@denx.de>
+ */
+
+/ {
+	wdt-reboot {
+		compatible = "wdt-reboot";
+		wdt = <&wdog1>;
+	};
+};