of: Add AU Optronics Corporation vendor prefix

AU Optronics is listed as AUO on the stock exchange, so use that as the
vendor prefix.
Signed-off-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NRob Herring <rob.herring@calxeda.com>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -12,6 +12,7 @@ amcc	Applied Micro Circuits Corporation (APM, formally AMCC)
 apm	Applied Micro Circuits Corporation (APM)
 arm	ARM Ltd.
 atmel	Atmel Corporation
+auo	AU Optronics Corporation
 avago	Avago Technologies
 bosch	Bosch Sensortec GmbH
 brcm	Broadcom Corporation