dt-bindings: vendor-prefixes: add Embest RIoT

Document vendor prefix for Embest RIoT.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200926162811.5335-3-krzk@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.yaml

@@ -890,6 +890,8 @@ patternProperties:
     description: Rikomagic Tech Corp. Ltd
   "^riscv,.*":
     description: RISC-V Foundation
+  "^riot,.*":
+    description: Embest RIoT
   "^rockchip,.*":
     description: Fuzhou Rockchip Electronics Co., Ltd
   "^rocktech,.*":