dt-bindings: display: convert samsung,s6e8aa0 to DT Schema

v2:
  - Add missing types (Rob)
  - Fix example to specify panel@0 (Rob)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200704102806.735713-3-sam@ravnborg.org