dt-bindings: riscv: Add SOPHGO Huashan Pi board compatibles

dt-bindings: riscv: Add SOPHGO Huashan Pi board compatibles

Document the compatible strings for the SOPHGO Huashan Pi board which
uses the SOPHGO CV1812H SoC.

Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Link: https://en.sophgo.com/product/introduce/huashan.html
Link: https://en.sophgo.com/product/introduce/cv181xH.html
Acked-by: Chen Wang <unicorn_wang@outlook.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>