usb: typec: altmodes/displayport: add support for embedded DP cases

In the embedded cases, the DisplayPort connector is handled by the TCPM
itself. It was proposed to add the "displayport" OF property to the DT
bindings, but it  was rejected in favour of properly describing the
electrical signal path using of_graph.

Fallback to the controller fwnode for HPD notifications to
support such usecases without requiring additional DT properties.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20230817150824.14371-2-dmitry.baryshkov@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>