dt-bindings: Add Siemens vendor prefix

Add prefix for Siemens AG.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/4750c25ded8d1d5791c14b0e7b450a2a918eea36.1615473223.git.jan.kiszka@siemens.com

Documentation/devicetree/bindings/vendor-prefixes.yaml

@@ -1024,6 +1024,8 @@ patternProperties:
     description: Silex Insight
   "^siliconmitus,.*":
     description: Silicon Mitus, Inc.
+  "^siemens,.*":
+    description: Siemens AG
   "^simtek,.*":
     description: Cypress Semiconductor Corporation (Simtek Corporation)
   "^sinlinx,.*":