arm64: dts: zynqmp: Add label for zynqmp_ipi

Add label which is used by bootloader for adding bootloader specific flag.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/3dc8416abdd3498e61edcd83830a12af295c5c6d.1611224800.git.michal.simek@xilinx.com

arch/arm64/boot/dts/xilinx/zynqmp.dtsi

@@ -99,7 +99,7 @@ opp03 {
 		};
 	};
 
-	zynqmp_ipi {
+	zynqmp_ipi: zynqmp_ipi {
 		compatible = "xlnx,zynqmp-ipi-mailbox";
 		interrupt-parent = <&gic>;
 		interrupts = <0 35 4>;