drm/msm/dp: move of_dp_aux_populate_bus() to eDP probe()

drm/msm/dp: move of_dp_aux_populate_bus() to eDP probe()

Currently eDP population is done at msm_dp_modeset_init() which happen
at binding time. Move eDP population to be done at display probe time
so that probe deferral cases can be handled effectively.
wait_for_hpd_asserted callback is added during drm_dp_aux_init()
to ensure eDP's HPD is up before proceeding eDP population.

Changes in v5:
-- inline dp_display_auxbus_population() and delete it

Changes in v4:
-- delete duplicate initialize code to dp_aux before drm_dp_aux_register()
-- delete of_get_child_by_name(dev->of_node, "aux-bus") and inline the
   function
-- not initialize rc = 0

Changes in v3:
-- add done_probing callback into devm_of_dp_aux_populate_bus()

Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/570074/
Link: https://lore.kernel.org/r/1701472789-25951-8-git-send-email-quic_khsieh@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>