doc: dt: add documentation for nxp,lpc1850-uart

Add device tree binding documentation for nxp,lpc1850-uart.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/nxp,lpc1850-uart.txt

@@ -0,0 +1,28 @@
+* NXP LPC1850 UART
+
+Required properties:
+- compatible	: "nxp,lpc1850-uart", "ns16550a".
+- reg		: offset and length of the register set for the device.
+- interrupts	: should contain uart interrupt.
+- clocks	: phandle to the input clocks.
+- clock-names	: required elements: "uartclk", "reg".
+
+Optional properties:
+- dmas		: Two or more DMA channel specifiers following the
+		  convention outlined in bindings/dma/dma.txt
+- dma-names	: Names for the dma channels, if present. There must
+		  be at least one channel named "tx" for transmit
+		  and named "rx" for receive.
+
+Since it's also possible to also use the of_serial.c driver all
+parameters from 8250.txt also apply but are optional.
+
+Example:
+uart0: serial@40081000 {
+	compatible = "nxp,lpc1850-uart", "ns16550a";
+	reg = <0x40081000 0x1000>;
+	reg-shift = <2>;
+	interrupts = <24>;
+	clocks = <&ccu2 CLK_APB0_UART0>, <&ccu1 CLK_CPU_UART0>;
+	clock-names = "uartclk", "reg";
+};