arm64: dts: marvell: armada-37xx: add mailbox node

This adds the rWTM BIU mailbox node for communication with the secure
processor. The driver already exists in
drivers/mailbox/armada-37xx-rwtm-mailbox.c.
Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: Gregory Clement <gregory.clement@bootlin.com>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>

arch/arm64/boot/dts/marvell/armada-37xx.dtsi

@@ -419,6 +419,13 @@ crypto: crypto@90000 {
 				clocks = <&nb_periph_clk 15>;
 			};
 
+			rwtm: mailbox@b0000 {
+				compatible = "marvell,armada-3700-rwtm-mailbox";
+				reg = <0xb0000 0x100>;
+				interrupts = <GIC_SPI 18 IRQ_TYPE_LEVEL_HIGH>;
+				#mbox-cells = <1>;
+			};
+
 			sdhci1: sdhci@d0000 {
 				compatible = "marvell,armada-3700-sdhci",
 					     "marvell,sdhci-xenon";