dt-bindings: arm: samsung: document Chagall WiFi board binding

Add binding for Samsung Galaxy Tab S 10.5", based on Exynos 5420 with
codename chagall-wifi. It was released in 2014 and has several siblings
with similar hardware.
Signed-off-by: NHenrik Grimler <henrik@grimler.se>
Link: https://lore.kernel.org/r/20220118185746.299832-2-henrik@grimler.seSigned-off-by: NKrzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

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

@@ -140,6 +140,7 @@ properties:
         items:
           - enum:
               - insignal,arndale-octa           # Insignal Arndale Octa
+              - samsung,chagall-wifi            # Samsung SM-T800
               - samsung,smdk5420                # Samsung SMDK5420 eval
           - const: samsung,exynos5420
           - const: samsung,exynos5