ARM: dts: sun8i: set cpu-supply in reference tablet DTSI

All reference design A33 tablets uses DCDC2 of AXP223 as the power
supply of the Cortex-A7 cores.

Set the cpu-supply in the DTSI of sun8i reference tablets.
Signed-off-by: NIcenowy Zheng <icenowy@aosc.xyz>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>

arch/arm/boot/dts/sun8i-reference-design-tablet.dtsi

@@ -214,6 +214,10 @@
 	regulator-name = "vcc-rtc";
 };
 
+&cpu0 {
+	cpu-supply = <&reg_dcdc2>;
+};
+
 &r_uart {
 	pinctrl-names = "default";
 	pinctrl-0 = <&r_uart_pins_a>;