dt-bindings: arm64: marvell: add solidrun cn9132 CEX-7 evaluation board

Add bindings for the SolidRun CN9132 COM-Express Type 7 evaluation board.
The CEX is based on CN9130 SoC and includes two southbridges.

Because CN9132 and 9131 are just names for different designs around the
same SoC, no soc compatibles beside marvell,cn9130 are needed.

Signed-off-by: Josua Mayer <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Signed-off-by: Gregory CLEMENT <[e-mail]>

Documentation/devicetree/bindings/arm/marvell/armada-7k-8k.yaml

···
           - const: solidrun,cn9130-sr-som
           - const: marvell,cn9130
 
+      - description:
+          SolidRun CN9132 COM-Express Type 7 based single-board computers
+        items:
+          - enum:
+              - solidrun,cn9132-clearfog
+          - const: solidrun,cn9132-sr-cex7
+          - const: marvell,cn9130
+
 additionalProperties: true