Documentation: Add EZchip vendor to binding list

Add EZchip to vendor prefixes list.
EZchip introduce the NPS platform for the ARC architecture.

Signed-off-by: Noam Camus <noamc@ezchip.com>
Acked-by: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>