ARM: dts: i.MX27: Add label to CPU node

Add a label to i.MX27 CPU node. This change allows the reuse this node
in the upper levels of the DTS.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx27.dtsi

@@ -53,7 +53,7 @@
 		#size-cells = <0>;
 		#address-cells = <1>;
 
-		cpu {
+		cpu: cpu@0 {
 			device_type = "cpu";
 			compatible = "arm,arm926ej-s";
 			operating-points = <