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

There are few bindings with compatibles starting with a "synopsys"
prefix. Document it as deprecated, to be sure no new usages will
appear.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/vendor-prefixes.yaml

···
     description: Synaptics Inc.
   "^synology,.*":
     description: Synology, Inc.
+  "^synopsys,.*":
+    description: Synopsys, Inc. (deprecated, use snps)
+    deprecated: true
   "^tbs,.*":
     description: TBS Technologies
   "^tbs-biometrics,.*":