dts: evb-rk3399: add init voltage node for vdd-center

Add a regulator-init-microvolt for vdd_center regulator
so that we can get a init value for driver probe.
Not like pmic regulator, the PWM regulator do not have a
known default output value, so we would like to init the
regulator when driver probe.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>

arch/arm/dts/rk3399-evb.dts

@@ -23,6 +23,7 @@
 		regulator-name = "vdd_center";
 		regulator-min-microvolt = <800000>;
 		regulator-max-microvolt = <1400000>;
+		regulator-init-microvolt = <950000>;
 		regulator-always-on;
 		regulator-boot-on;
 		status = "okay";