ASoC: dt-bindings: samsung,arndale: document ALC5631

The Arndale audio complex might come with ALC5631 which is compatible
with RT5631.  Document the compatible since it is used in Linux kernel
sources.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220129122430.45694-2-krzysztof.kozlowski@canonical.com
Signed-off-by: Mark Brown <broonie@kernel.org>