warp7: Convert to watchdog driver model

Commit 68dcbdd594d4 ("ARM: imx: Add weak default reset_cpu()") caused
the 'reset' command in U-Boot to not cause a board reset.

Fix it by switching to the watchdog driver model via sysreset, which
is the preferred method for implementing the watchdog reset.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/dts/imx7s-warp-u-boot.dtsi b/arch/arm/dts/imx7s-warp-u-boot.dtsi
index 4f44598..98784fd 100644
--- a/arch/arm/dts/imx7s-warp-u-boot.dtsi
+++ b/arch/arm/dts/imx7s-warp-u-boot.dtsi
@@ -7,6 +7,12 @@
 	chosen {
 		stdout-path = &uart1;
 	};
+
+	wdt-reboot {
+		compatible = "wdt-reboot";
+		wdt = <&wdog1>;
+		bootph-pre-ram;
+	};
 };
 
 &aips3 {
@@ -24,3 +30,7 @@
 &uart1 {
 	bootph-all;
 };
+
+&wdog1 {
+	bootph-pre-ram;
+};