dt: document NXP LPC1850 DAC driver bindings

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/dac/lpc1850-dac.txt

+NXP LPC1850 DAC bindings
+
+Required properties:
+- compatible: Should be "nxp,lpc1850-dac"
+- reg: Offset and length of the register set for the ADC device
+- interrupts: The interrupt number for the ADC device
+- clocks: The root clock of the ADC controller
+- vref-supply: The regulator supply ADC reference voltage
+- resets: phandle to reset controller and line specifier
+
+Example:
+dac: dac@400e1000 {
+	compatible = "nxp,lpc1850-dac";
+	reg = <0x400e1000 0x1000>;
+	interrupts = <0>;
+	clocks = <&ccu1 CLK_APB3_DAC>;
+	vref-supply = <&reg_vdda>;
+	resets = <&rgu 42>;
+	status = "disabled";
+};