ARM: dts: add vendor prefix for cubietech

Add a cubietech vendor prefix, as it is missing. The cubietruck, cubieboard2,
and cubieboard all already reference this prefix.
Signed-off-by: Tyler Baker <tyler.baker@linaro.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -52,6 +52,7 @@ cnxt	Conexant Systems, Inc.
 cortina	Cortina Systems, Inc.
 cosmic	Cosmic Circuits
 crystalfontz	Crystalfontz America, Inc.
+cubietech	Cubietech, Ltd.
 dallas	Maxim Integrated Products (formerly Dallas Semiconductor)
 davicom	DAVICOM Semiconductor, Inc.
 denx	Denx Software Engineering