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 | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/riscv/boot/dts/thead/th1520.dtsi b/arch/riscv/boot/dts/thead/th1520.dtsi
index 3c9974062c20..5d0cc1d899d7 100644
--- a/arch/riscv/boot/dts/thead/th1520.dtsi
+++ b/arch/riscv/boot/dts/thead/th1520.dtsi
@@ -546,5 +546,20 @@ portf: gpio-controller@0 {
 				interrupts = <55 IRQ_TYPE_LEVEL_HIGH>;
 			};
 		};
+
+		mbox_910t: mbox@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_base", "remote_icu0", "remote_icu1", "remote_icu2";
+		       interrupt-parent = <&plic>;
+		       interrupts = <28 IRQ_TYPE_LEVEL_HIGH>;
+		       clocks = <&apb_clk>;
+		       clock-names = "ipg";
+		       icu_cpu_id = <0>;
+		       #mbox-cells = <2>;
+		};
 	};
 };
-- 
2.34.1