dt-bindings: drm/panel: Document Innolux TV123WAM panel bindings

Innolux TV123WAM is a 12.3" eDP display panel with
2160x1440 resolution, which can be supported by simple
panel driver.

Changes in v1:
 - Make use of simple panel driver instead of creating
   a new driver for this panel (Sean Paul).
 - Combine dt-binding and driver changes into one patch
   as done by other existing panel support changes.

Changes in v2:
 - Separate driver change from dt-binding documentation (Rob Herring).
 - Add the properties from simple-panel binding that are applicable to
   this panel (Rob Herring).

Signed-off-by: Sandeep Panda <spanda@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1526363564-13823-5-git-send-email-spanda@codeaurora.org