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>