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 <[e-mail]>
Signed-off-by: Vineet Gupta <[e-mail]>

arch/arc/boot/dts/skeleton.dtsi

···
 			device_type = "cpu";
 			compatible = "snps,arc770d";
 			reg = <0>;
+			clocks = <&core_clk>;
 		};
 	};
 

arch/arc/boot/dts/skeleton_hs.dtsi

···
 			device_type = "cpu";
 			compatible = "snps,archs38";
 			reg = <0>;
+			clocks = <&core_clk>;
 		};
 	};
 

arch/arc/boot/dts/skeleton_hs_idu.dtsi

···
 			device_type = "cpu";
 			compatible = "snps,archs38xN";
 			reg = <0>;
+			clocks = <&core_clk>;
 		};
 	};