dt-bindings: arm: fsl: add Variscite DART-MX91 Boards

Add DT compatible strings for Variscite DART-MX91 SoM and Variscite
development carrier Board.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Stefano Radaelli <stefano.r@variscite.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>

Author: StefanoRadaelliVar

Documentation/devicetree/bindings/arm/fsl.yaml

@@ -1552,6 +1552,12 @@ properties:
           - const: phytec,imx93-phycore-som # phyCORE-i.MX93 SoM
           - const: fsl,imx93
 
+      - description: Variscite DART-MX91 based boards
+        items:
+          - const: variscite,var-dart-mx91-sonata # Variscite DART-MX91 on Sonata Development Board
+          - const: variscite,var-dart-mx91 # Variscite DART-MX91 SOM
+          - const: fsl,imx91
+
       - description: Variscite VAR-SOM-MX93 based boards
         items:
           - const: variscite,var-som-mx93-symphony