ARM: dts: imx25/27-eukrea: Fix RTC node name

Node names should be generic. Use 'rtc' as node name to fix
the following dt-schema warning:

imx25-eukrea-mbimxsd25-baseboard.dtb: pcf8563@51: $nodename:0: 'pcf8563@51' does not match '^rtc(@.*|-([0-9]|[1-9][0-9]+))?$'
	from schema $id: http://devicetree.org/schemas/rtc/nxp,pcf8563.yaml#Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/nxp/imx/imx25-eukrea-cpuimx25.dtsi

@@ -27,7 +27,7 @@ &i2c1 {
 	pinctrl-0 = <&pinctrl_i2c1>;
 	status = "okay";
 
-	pcf8563@51 {
+	rtc@51 {
 		compatible = "nxp,pcf8563";
 		reg = <0x51>;
 	};

arch/arm/boot/dts/nxp/imx/imx27-eukrea-cpuimx27.dtsi

@@ -33,7 +33,7 @@ &i2c1 {
 	pinctrl-0 = <&pinctrl_i2c1>;
 	status = "okay";
 
-	pcf8563@51 {
+	rtc@51 {
 		compatible = "nxp,pcf8563";
 		reg = <0x51>;
 	};