arm64: dts: rockchip: move rock 5b to include file

Radxa released some more boards, which are based on the original
Rock 5B. Move its board description into an include file to avoid
unnecessary duplication.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20250508-rock5bp-for-upstream-v2-1-677033cc1ac2@kernel.org
Link: https://lore.kernel.org/r/20250508-rock5bp-for-upstream-v2-2-677033cc1ac2@kernel.org



[The original submission was split into two elements, renaming the file
 and then moving some nodes around. This was done to make review easier
 due to the diff being smaller. This commit is a squash of both of them
 to facilitate bisectability and was also intended by the original author]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>