dt-bindings: arm: rockchip: Add Radxa ROCK 3B

Add devicetree binding documentation for the Radxa ROCK 3B board.

The Radxa ROCK 3B is a single-board computer based on the Pico-ITX form
factor (100mm x 75mm). Two versions of the ROCK 3B exists, a community
version based on the RK3568 SoC and an industrial version based on the
RK3568J SoC.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240627211737.1985549-2-jonas@kwiboo.se
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Author: Kwiboo

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -811,6 +811,11 @@ properties:
           - const: radxa,rock3a
           - const: rockchip,rk3568
 
+      - description: Radxa ROCK 3B
+        items:
+          - const: radxa,rock-3b
+          - const: rockchip,rk3568
+
       - description: Radxa ROCK 3C
         items:
           - const: radxa,rock-3c