dt-bindings: arm: rockchip: add Anbernic RG353PS

Add devicetree binding for Anbernic RG353PS. This device is identical
to the RG353P, except it does not have a touchscreen, does not have
an eMMC, only includes 1GB of RAM, and ships with only the 2nd
revision panel based on a Sitronix ST7703 controller. Support for the
panel has been added in a separate commit.

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230512162039.31132-2-macroalpha82@gmail.com


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