LF-4744: drm: bridge: cdns-dp: init drm_dp_aux->drm_dev

commit d32d07028f2759513b3f3b46591d6a5fba2cffd9 from
https://github.com/nxp-imx/linux-imx

drm_dp_aux->drm_dev was introduced by the followed patch.
init it to avoid kernel dump.

Author: Lyude Paul <lyude@redhat.com>
Date:   Fri Apr 23 14:42:55 2021 -0400

    drm/dp: Add backpointer to drm_device in drm_dp_aux

    This is something that we've wanted for a while now: the ability to
    actually look up the respective drm_device for a given drm_dp_aux struct.
    This will also allow us to transition over to using the drm_dbg_*() helpers
    for debug message printing, as we'll finally have a drm_device to reference
    for doing so.

    Note that there is one limitation with this - because some DP AUX adapters
    exist as platform devices which are initialized independently of their
    respective DRM devices, one cannot rely on drm_dp_aux->drm_dev to always be
    non-NULL until drm_dp_aux_register() has been called. We make sure to point
    this out in the documentation for struct drm_dp_aux.

    v3:
    * Add WARN_ON_ONCE() to drm_dp_aux_register() if drm_dev isn't filled out

Signed-off-by: Lyude Paul <lyude@redhat.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>

Signed-off-by: Sandor Yu <Sandor.yu@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>