dt-bindings: Add vendor prefixes

dt-bindings: Add vendor prefixes

These vendor prefixes are used by some routers supported
by e.g. OpenWrt.

- ADI Engineering is a US telecom equipment company.

- Arcom Controllers is a US manufacturer of repeaters.

- Freecom Gmbh is a german telecom equipment company.

- Gemtek Technology is a Taiwan telecom company.

- Gateway Communications was a telecommunication company,
  now acquired by HKT Limited/PCCW.

- Goramo Gorecki is a privately owned Polish telecom
  company.

- U.S. Robotics Corporation, known through their brand name
  USRobotics is generally referred to as "USR" so use this
  prefix for the company's device tree bindings.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20231007-ixp4xx-usr8200-v3-1-ec46edd1ff0e@linaro.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>