As the binding matches panel-simple-dsi, added the compatible to the
panel-simple-dsi list.
With this change enable-gpios is now optional.

v2:
  - It is a DSI panel, add it to panel-simple-dsi (Rob)
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Chris Zhong <zyw@rock-chips.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200704102806.735713-2-sam@ravnborg.org