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: Henrik Grimler <henrik@grimler.se>
Link: https://lore.kernel.org/r/20220118185746.299832-2-henrik@grimler.se


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>