arm64: dts: rockchip: Add BigTreeTech CB2 and Pi2

BigTreeTech CB2 and Pi2 share a lot of hardware configuration, so a
common dtsi file was used to define common nodes and properties. This is
similar to how BigTreeTech CB1 and Pi are implemented.

Signed-off-by: Ivan Sergeev <ivan8215145640@gmail.com>
Link: https://lore.kernel.org/r/20250106-bigtreetech-cb2-v7-2-565567e2c0a4@gmail.com


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