board: rockchip: Add support for new boards to RGxx3

Add support for the Anbernic RG-ARC-D, Anbernic RG-ARC-S, Powkiddy
RK2023, and Powkiddy RGB30 to the Anbernic RGxx3. While the Powkiddy
devices are manufactured by Powkiddy instead of Anbernic,
the hardware is so similar they can all use the same bootloader.

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