dt-bindings: display: convert boe,himax8279d to DT Schema

v2:
  - Fix entry in MAINTAINERS

v3:
  - Fix panel@0 in example (Rob)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Jerry Han <hanxu5@huaqin.corp-partner.google.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200408195109.32692-7-sam@ravnborg.org