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>

Documentation/devicetree/bindings/arc/eznps.txt

@@ -0,0 +1,7 @@
+EZchip NPS Network Processor Platforms Device Tree Bindings
+---------------------------------------------------------------------------
+
+Appliance main board with NPS400 ASIC.
+
+Required root node properties:
+    - compatible = "ezchip,arc-nps";