dt-bindings: arm: sunxi: document Anbernic RG35XX handheld gaming device variants

RG35XX 2024: Base version with Allwinner H700
RG35XX Plus: Adds Wifi/BT
RG35XX H: Adds second USB port and analog sticks to -Plus in horizontal form factor

Use three separate device descriptions rather than enum as per existing sunxi binding style.

Signed-off-by: Ryan Walklin <ryan@testtoast.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240427110225.727472-4-ryan@testtoast.com
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>