arm64: dts: rockchip: Add rk3368 mailbox device nodes

This adds mailbox device nodes in dts.

Mailbox is used by the Rockchip CPU cores to communicate
requests to MCU processor.
Signed-off-by: NCaesar Wang <wxt@rock-chips.com>
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3368.dtsi

@@ -555,6 +555,18 @@
 		status = "disabled";
 	};
 
+	mbox: mbox@ff6b0000 {
+		compatible = "rockchip,rk3368-mailbox";
+		reg = <0x0 0xff6b0000 0x0 0x1000>;
+		interrupts = <GIC_SPI 146 IRQ_TYPE_LEVEL_HIGH>,
+			     <GIC_SPI 147 IRQ_TYPE_LEVEL_HIGH>,
+			     <GIC_SPI 148 IRQ_TYPE_LEVEL_HIGH>,
+			     <GIC_SPI 149 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&cru PCLK_MAILBOX>;
+		clock-names = "pclk_mailbox";
+		#mbox-cells = <1>;
+	};
+
 	pmugrf: syscon@ff738000 {
 		compatible = "rockchip,rk3368-pmugrf", "syscon";
 		reg = <0x0 0xff738000 0x0 0x1000>;