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