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

Documentation/devicetree/bindings/arm/sprd/sprd.yaml

@@ -35,6 +35,11 @@ properties:
               - sprd,ums512-1h10
           - const: sprd,ums512
 
+      - items:
+          - enum:
+              - sprd,ums9620-2h10
+          - const: sprd,ums9620
+
 additionalProperties: true
 
 ...