ARC: [dts] add input clocks for cpu nodes

ARC CPU cores are driven by core_clk so we add corresponding "clocks"
property to ARC cpu nodes.

Signed-off-by: Vlad Zakharov <vzakhar@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/boot/dts/skeleton.dtsi

@@ -26,6 +26,7 @@
 			device_type = "cpu";
 			compatible = "snps,arc770d";
 			reg = <0>;
+			clocks = <&core_clk>;
 		};
 	};