dt-bindings: Add Truly NT35597 panel driver bindings

Add the device tree bindings for Truly NT35597 panel driver. This panel
driver supports both single DSI and dual DSI.

However, this patch series supports only dual DSI.

Changes in v10:
  - Remove active high in the documentation for mode gpio
  - Fix commmit text detail about the board and also
    fix a typo

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1538787139-28122-2-git-send-email-abhinavk@codeaurora.org