dt-bindings: vendor-prefixes: add Siflower

Shanghai Siflower Communication Co. is a manufacturer for home router SoCs.
Add a vendor prefix for it.

Link: http://www.siflower.com.cn/en
Signed-off-by: Chuanhong Guo <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring (Arm) <[e-mail]>

Documentation/devicetree/bindings/vendor-prefixes.yaml

···
     description: Siemens AG
   "^sifive,.*":
     description: SiFive, Inc.
+  "^siflower,.*":
+    description: Shanghai Siflower Communication Co.
   "^sigma,.*":
     description: Sigma Designs, Inc.
   "^sii,.*":