arm64: dts: ti: k3-am64-main: Add main_cpts label

Makes it easier to reference the node in board dts files.
Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20220822095943.18563-1-christian.gmeiner@gmail.com

arch/arm64/boot/dts/ti/k3-am64-main.dtsi

@@ -550,7 +550,7 @@ cpts@3d000 {
 		};
 	};
 
-	cpts@39000000 {
+	main_cpts0: cpts@39000000 {
 		compatible = "ti,j721e-cpts";
 		reg = <0x0 0x39000000 0x0 0x400>;
 		reg-names = "cpts";