dt-bindings: riscv: spacemit: Add OrangePi RV2 board

dt-bindings: riscv: spacemit: Add OrangePi RV2 board

Document the compatible string 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].

Link: http://www.orangepi.org/html/hardWare/computerAndMicrocontrollers/details/Orange-Pi-RV2.html
Link: https://www.spacemit.com/en/key-stone-k1
Signed-off-by: Hendrik Hamerlinck <hendrik.hamerlinck@hammernet.be>
Reviewed-by: Yixun Lan <dlan@gentoo.org>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250813092240.180333-2-hendrik.hamerlinck@hammernet.be
Signed-off-by: Yixun Lan <dlan@gentoo.org>