dt-bindings: vendor-prefixes: Add Beacon vendor prefix

Beacon EmebeddedWorks is the brand owned by Compass Electronics Group,
LLC based out of the United States.
https://beaconembedded.com/



Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>