ARM: dts: imx7s: add i.MX7 messaging unit support

Define the Messaging Unit (MU) for i.MX7 in the processor's dtsi.
The respective driver is added in the next commit.
Reviewed-by: NDong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: NOleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx7s.dtsi

@@ -974,6 +974,25 @@
 				status = "disabled";
 			};
 
+			mu0a: mailbox@30aa0000 {
+				compatible = "fsl,imx7s-mu", "fsl,imx6sx-mu";
+				reg = <0x30aa0000 0x10000>;
+				interrupts = <GIC_SPI 88 IRQ_TYPE_LEVEL_HIGH>;
+				clocks = <&clks IMX7D_MU_ROOT_CLK>;
+				#mbox-cells = <2>;
+				status = "disabled";
+			};
+
+			mu0b: mailbox@30ab0000 {
+				compatible = "fsl,imx7s-mu", "fsl,imx6sx-mu";
+				reg = <0x30ab0000 0x10000>;
+				interrupts = <GIC_SPI 97 IRQ_TYPE_LEVEL_HIGH>;
+				clocks = <&clks IMX7D_MU_ROOT_CLK>;
+				#mbox-cells = <2>;
+				fsl,mu-side-b;
+				status = "disabled";
+			};
+
 			usbotg1: usb@30b10000 {
 				compatible = "fsl,imx7d-usb", "fsl,imx27-usb";
 				reg = <0x30b10000 0x200>;