dt-bindings: vendor-prefixes: Add Titan Micro Electronics

Assign vendor prefix "titanmec", matching their domain name.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>