arm64: dts: apm: Mailbox device tree node for APM X-Gene v2 platform.

Add mailbox device tree node for APM X-Gene v2 platform.
Signed-off-by: Duc Dang <dhdang@apm.com>

arch/arm64/boot/dts/apm/apm-shadowcat.dtsi

@@ -453,6 +453,20 @@ edacsoc@7e930000 {
 			};
 		};
 
+		mailbox: mailbox@10540000 {
+			compatible = "apm,xgene-slimpro-mbox";
+			reg = <0x0 0x10540000 0x0 0x8000>;
+			#mbox-cells = <1>;
+			interrupts =   <0x0 0x0 0x4
+					0x0 0x1 0x4
+					0x0 0x2 0x4
+					0x0 0x3 0x4
+					0x0 0x4 0x4
+					0x0 0x5 0x4
+					0x0 0x6 0x4
+					0x0 0x7 0x4>;
+		};
+
 		serial0: serial@10600000 {
 			device_type = "serial";
 			compatible = "ns16550";