dt/bindings: add binding for ARM Versatile character LCD

Add binding doc for Versatile platforms character LCD controller
interface.
Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/misc/arm-charlcd.txt

+ARM Versatile Character LCD
+-----------------------------------------------------
+This binding defines the character LCD interface found on ARM Versatile AB
+and PB reference platforms.
+
+Required properties:
+- compatible : "arm,versatile-clcd"
+- reg : Location and size of character LCD registers
+
+Optional properties:
+- interrupts - single interrupt for character LCD. The character LCD can
+  operate in polled mode without an interrupt.
+
+Example:
+	lcd@10008000 {
+		compatible = "arm,versatile-lcd";
+		reg = <0x10008000 0x1000>;
+	};