drm/panel-edp: Take advantage of wait_hpd_asserted() in struct drm_dp_aux

Let's add support for being able to read the HPD pin even if it's
hooked directly to the controller. This will allow us to get more
accurate delays also lets us take away the waiting in the AUX transfer
functions of the eDP controller drivers.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220614145327.v4.2.Icea616f57331fbaa3d48c529f300c9a8ebd37fb5@changeid