dt-bindings: tc358767: add HPD support

Add DT property for defining the pin used for HPD.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: devicetree@vger.kernel.org
Cc: Rob Herring <robh@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528082747.3631-25-tomi.valkeinen@ti.com

Documentation/devicetree/bindings/display/bridge/toshiba,tc358767.txt

@@ -12,6 +12,7 @@ Optional properties:
                    (active high shutdown input)
  - reset-gpios: OF device-tree gpio specification for RSTX pin
                 (active low system reset)
+ - toshiba,hpd-pin: TC358767 GPIO pin number to which HPD is connected to (0 or 1)
  - ports: the ports node can contain video interface port nodes to connect
    to a DPI/DSI source and to an eDP/DP sink according to [1][2]:
     - port@0: DSI input port