devicetree: Add vendor-prefix for DH electronics GmbH

Add vendor prefix for DH electronics GmbH, https://www.dh-electronics.com .
The company is a SoM and evaluation board manufacturer.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -83,6 +83,7 @@ davicom	DAVICOM Semiconductor, Inc.
 delta	Delta Electronics, Inc.
 denx	Denx Software Engineering
 devantech	Devantech, Ltd.
+dh	DH electronics GmbH
 digi	Digi International Inc.
 digilent	Diglent, Inc.
 dioo	Dioo Microcircuit Co., Ltd