dt-bindings: display: Document FriendlyELEC HD702E LCD panel

dt-bindings: display: Document FriendlyELEC HD702E LCD panel

HD702E lcd is FriendlyELEC developed eDP LCD panel with 800x1280
resolution. It has built in Goodix, GT9271 captive touchscreen
with backlight adjustable via PWM.

Add dt-bindings documentation for it.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190507130708.11255-1-jagan@amarulasolutions.com