dt-bindings: arm: rockchip: add Radxa CM3I E25

Radxa CM3 Industrial (CM3I) is an System on Module made by Radxa
based on the Rockchip RK3568 SoC. The first carrier board supported
is the Radxa E25. Add devicetree binding documentation for it.

Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221209102524.129367-2-amadeus@jmu.edu.cn


Signed-off-by: Heiko Stuebner <heiko@sntech.de>