dt-bindings: arm: at91: Document Kizbox3 HS board binding

Document devicetree binding of SAMA5D27 Kizbox3 HS board from Overkiz
SAS.
Signed-off-by: Kamel Bouhara <kamel.bouhara@bootlin.com>
Link: https://lore.kernel.org/r/20191011125022.16329-3-kamel.bouhara@bootlin.comReviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/arm/atmel-at91.yaml

@@ -45,6 +45,13 @@ properties:
           - const: atmel,at91sam9x5
           - const: atmel,at91sam9
 
+      - description: Overkiz kizbox3 board
+        items:
+          - const: overkiz,kizbox3-hs
+          - const: atmel,sama5d27
+          - const: atmel,sama5d2
+          - const: atmel,sama5
+
       - items:
           - const: atmel,sama5d27
           - const: atmel,sama5d2