Add devicetree binding documentation for Radxa ZERO 3W/3E boards.

The Radxa ZERO 3W/3E is an ultra-small, high-performance single board
computer based on the Rockchip RK3566, with a compact form factor and
rich interfaces.
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240521202810.1225636-2-jonas@kwiboo.seSigned-off-by: Heiko Stuebner <heiko@sntech.de>