dt-bindings: Add RDA Micro vendor prefix

Add vendor prefix for RDA Micro which now merged into Unisoc
Communications Inc.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -320,6 +320,7 @@ ralink	Mediatek/Ralink Technology Corp.
 ramtron	Ramtron International
 raspberrypi	Raspberry Pi Foundation
 raydium	Raydium Semiconductor Corp.
+rda	Unisoc Communications, Inc.
 realtek Realtek Semiconductor Corp.
 renesas	Renesas Electronics Corporation
 richtek	Richtek Technology Corporation