riscv: dts: spacemit: Add OrangePi R2S board device tree

riscv: dts: spacemit: Add OrangePi R2S board device tree

Add initial device tree support for the OrangePi RV2 board [1], which is
marketed as using the Ky X1 SoC but is identical in die and package
to the SpacemiT K1 SoC [2].

Enable UART0, to boot into a serial console

Two Gigabit Ethernet ports with RGMII interface standard support
are enabled, each port is connected to an external
Motorcomm YT8531C PHY chip which uses the GPIO for reset control.

Enable PDMA.

Enable 8 GB eMMC chip for storage.

Link: http://www.orangepi.org/html/hardWare/computerAndMicrocontrollers/details/Orange-Pi-R2S.html
Link: https://www.spacemit.com/en/key-stone-k1
Signed-off-by: Michael Opdenacker <michael.opdenacker@rootcommit.com>
Reviewed-by: Yixun Lan <dlan@gentoo.org>
Link: https://lore.kernel.org/r/20251112044426.2351999-3-michael.opdenacker@rootcommit.com
Signed-off-by: Yixun Lan <dlan@gentoo.org>