ARM: dt-bindings: Add vendor prefix for Facebook

Initial introduction of Facebook TiogaPass family equipped with
Aspeed 2500 BMC SoC. TiogaPass is a x86 server development kit
with a ASPEED ast2500 BMC manufactured by Facebook.

This adds an entry of Facebook in Documentation for vendor prefix
Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -127,6 +127,7 @@ everspin	Everspin Technologies, Inc.
 exar	Exar Corporation
 excito	Excito
 ezchip	EZchip Semiconductor
+facebook	Facebook
 fairphone	Fairphone B.V.
 faraday	Faraday Technology Corporation
 fastrax	Fastrax Oy