dt-bindings: vendor-prefixes: document Powkiddy

Document Powkiddy (https://powkiddy.com/).

Signed-off-by: Chris Morgan <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Heiko Stuebner <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/devicetree/bindings/vendor-prefixes.yaml

···
     description: Powertip Tech. Corp.
   "^powervr,.*":
     description: PowerVR (deprecated, use img)
+  "^powkiddy,.*":
+    description: Powkiddy
   "^primux,.*":
     description: Primux Trading, S.L.
   "^probox2,.*":