dt-bindings: arm: Add compatible strings for Unisoc's UMS9620

Added bindings for Unisoc's UMS9620-2H10 board and UMS9620 SoC.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231218100234.1102916-3-chunyan.zhang@unisoc.com


Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>