ARM: dts: imx6: RDU2: Add RAVE SP device

With MFD and watchdog drivers for RAVE SP device support added by
538ee27290fa ("mfd: Add driver for RAVE Supervisory Processor") and
c3bb33345721 ("watchdog: Add RAVE SP watchdog driver") add
corresponding DT node for RDU2.

Cc: Rob Herring <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Guenter Roeck <[e-mail]>
Cc: Chris Healy <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Andrey Smirnov <[e-mail]>
Reviewed-by: Fabio Estevam <[e-mail]>
Reviewed-by: Lucas Stach <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi

···
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_uart4>;
 	status = "okay";
+
+	rave-sp {
+		compatible = "zii,rave-sp-rdu2";
+		current-speed = <1000000>;
+
+		watchdog {
+			compatible = "zii,rave-sp-watchdog";
+		};
+	};
 };
 
 &ecspi1 {