dt-bindings: display: panel: Add binding document for Xinpeng XPP055C272

The XPP055C272 is a 5.5" 720x1280 DSI display.

changes in v4:
- fix id (Maxime)
- drop port (Maxime)
changes in v2:
- add size info into binding title (Sam)
- add more required properties (Sam)

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191224112907.30758-2-heiko@sntech.de