dt-bindings: arm: samsung: Document exynosautov920 SADK board binding

Add binding for the ExynosAutov920 SADK(Samsung Automotive Development Kit)
board.

Signed-off-by: Jaewon Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>

Documentation/devicetree/bindings/arm/samsung/samsung-boards.yaml

···
               - samsung,exynosautov9-sadk   # Samsung Exynos Auto v9 SADK
           - const: samsung,exynosautov9
 
+      - description: Exynos Auto v920 based boards
+        items:
+          - enum:
+              - samsung,exynosautov920-sadk   # Samsung Exynos Auto v920 SADK
+          - const: samsung,exynosautov920
+
 required:
   - compatible