dt-bindings: vendor-prefixes: add "virtual" prefix

"virtual" is used for vendor-less "devices". For example for the GPIO
based MDIO bus "virtual,mdio-gpio".

This patch is needed to fix the checkpatch warning for the Protonic WD3 board.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
diff --git a/Documentation/devicetree/bindings/vendor-prefixes.yaml b/Documentation/devicetree/bindings/vendor-prefixes.yaml
index 8db0ab3..6a9be2b 100644
--- a/Documentation/devicetree/bindings/vendor-prefixes.yaml
+++ b/Documentation/devicetree/bindings/vendor-prefixes.yaml
@@ -1158,6 +1158,8 @@
     description: Videostrong Technology Co., Ltd.
   "^virtio,.*":
     description: Virtual I/O Device Specification, developed by the OASIS consortium
+  "^virtual,.*":
+    description: Used for virtual device without specific vendor.
   "^vishay,.*":
     description: Vishay Intertechnology, Inc
   "^vitesse,.*":