dt-bindings: vendor-prefixes: Add an entry for OpenEmbed

Add "openembed" entry for https://www.openembed.com/



Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>