dt-bindings: add vendor TPO

TPO was a merger on June 5 2006 of Toppoly Optoelectronics and
Philips Mobile Display Systems. They manufactured small and medium
mobile displays.
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -270,6 +270,7 @@ toshiba	Toshiba Corporation
 toumaz	Toumaz
 tplink	TP-LINK Technologies Co., Ltd.
 tpk	TPK U.S.A. LLC
+tpo	TPO
 tronfy	Tronfy
 tronsmart	Tronsmart
 truly	Truly Semiconductors Limited