dt-bindings: vendor-prefixes: add prefix for admatec GmbH

admatec GmbH is a german supplier for industrial displays.

Link: https://www.admatec.de/


Signed-off-by: Heiko Stuebner <heiko.stuebner@cherry.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240215090442.3513760-1-heiko@sntech.de