dt-bindings: display: convert kingdisplay,kd097d04 to DT Schema

kingdisplay,kd097d04 matches the panel-simple-dsi binding.
The only difference is that enable-gpios is now an optional
property.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Nickey Yang <nickey.yang@rock-chips.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200408195109.32692-15-sam@ravnborg.org