dt-bindings: display: convert simple lg panels to DT Schema

Add the lg panels that matches the panel-simple binding to
panel-simple.yaml

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Brian Masney <masneyb@onstation.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Brian Masney <masneyb@onstation.org>
Cc: Alexandre Courbot <acourbot@chromium.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200408195109.32692-16-sam@ravnborg.org