dt-bindings: Add vendor prefix for Engleder

Engleder develops FPGA based controllers for real-time communication.

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>