dt-bindings: vendor-prefixes: add second HiSilicon prefix

There are few boards DTS using "hisi,rst-syscon" property -
undocumented "hisi" prefix.  The property will not be changed in DTS to
non-deprecated one, because of compatibility reasons.  Add deprecated
"hisi" prefix to silence DT schema warnings.

Cc: Wei Xu <xuwei5@hisilicon.com>
Cc: David Heidelberg <david@ixit.cz>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: David Heidelberg <david@ixit.cz>
Reviewed-by: Wei Xu <xuwei5@hisilicon.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220221082228.34407-1-krzysztof.kozlowski@canonical.com

Documentation/devicetree/bindings/vendor-prefixes.yaml

@@ -499,6 +499,9 @@ patternProperties:
     description: Himax Technologies, Inc.
   "^hirschmann,.*":
     description: Hirschmann Automation and Control GmbH
+  "^hisi,.*":
+    description: HiSilicon Limited (deprecated, use hisilicon)
+    deprecated: true
   "^hisilicon,.*":
     description: HiSilicon Limited.
   "^hit,.*":