board: rockchip: Convert Anbernic RGxx3 to OF_UPSTREAM

Refactor the board detection logic (again) to make it compatible with
the upstream device-trees, and switch to OF_UPSTREAM.

Now the device boots with the device-tree for the 353P, and then
loads the correct device tree (of 10) in the later stages of SPL.

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
6 files changed