drm/panel: Add DT bindings for Sony ACX424AKP

This adds device tree bindings for the Sony ACX424AKP panel.
Let's use YAML.

Cc: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191114131525.3988-1-linus.walleij@linaro.org