riscv: dts: spacemit: Add OrangePi RV2 board device tree

riscv: dts: spacemit: Add OrangePi RV2 board device tree

Add initial device tree support for the OrangePi RV2 board [1]. The board
is described as using the Ky X1 SoC, which, based on available downstream
sources and testing, appears to be identical or very closely related to
the SpacemiT K1 SoC [2].

The device tree is adapted from the OrangePi vendor tree [3], and similar
integration can be found in the Banana Pi kernel tree [4], confirming SoC
compatibility. The main difference with the current Banana Pi BPI-F3 tree
is that status led is using GPIO_ACTIVE_LOW.

This minimal device tree enables booting into a serial console with UART
output and a blinking LED.

Link: http://www.orangepi.org/html/hardWare/computerAndMicrocontrollers/details/Orange-Pi-RV2.html
Link: https://www.spacemit.com/en/key-stone-k1
Link: https://github.com/BPI-SINOVOIP/pi-linux/blob/linux-6.6.63-k1/arch/riscv/boot/dts/spacemit/k1-x_orangepi-rv2.dts
Link: https://github.com/orangepi-xunlong/linux-orangepi/tree/orange-pi-6.6-ky
Signed-off-by: Hendrik Hamerlinck <hendrik.hamerlinck@hammernet.be>
Reviewed-by: Yixun Lan <dlan@gentoo.org>
Link: https://lore.kernel.org/r/20250813092240.180333-3-hendrik.hamerlinck@hammernet.be
Signed-off-by: Yixun Lan <dlan@gentoo.org>