Add mailbox device tree node. This work is based on the vendor kernel [1].

Link: https://github.com/revyos/thead-kernel.git [1]

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 arch/riscv/boot/dts/thead/th1520.dtsi | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/riscv/boot/dts/thead/th1520.dtsi b/arch/riscv/boot/dts/thead/th1520.dtsi
index 6992060e6a54..435f0ab0174d 100644
--- a/arch/riscv/boot/dts/thead/th1520.dtsi
+++ b/arch/riscv/boot/dts/thead/th1520.dtsi
@@ -555,5 +555,17 @@ portf: gpio-controller@0 {
 				interrupts = <55 IRQ_TYPE_LEVEL_HIGH>;
 			};
 		};
+
+		mbox_910t: mailbox@ffffc38000 {
+		       compatible = "thead,th1520-mbox";
+		       reg = <0xff 0xffc38000 0x0 0x4000>,
+			     <0xff 0xffc44000 0x0 0x1000>,
+			     <0xff 0xffc4c000 0x0 0x1000>,
+			     <0xff 0xffc54000 0x0 0x1000>;
+		       reg-names = "local", "remote-icu0", "remote-icu1", "remote-icu2";
+		       interrupt-parent = <&plic>;
+		       interrupts = <28 IRQ_TYPE_LEVEL_HIGH>;
+		       #mbox-cells = <2>;
+		};
 	};
 };
-- 
2.34.1