drm/rockchip: cdn-dp: do not use drm_helper_hpd_irq_event

The cdn_dp_pd_event_work is using drm_helper_hpd_irq_event to update the
connector status, this function is used to update all connectors of
drm_device. Therefore, the detect of other connector will be call, when
cdn_dp_pd_event_work is triggered, every time. It is not necessary, and
it may cause system crash. replace drm_helper_hpd_irq_event with
drm_kms_helper_hotplug_event, only update cdn-dp status.

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Tested-by: Guenter Roeck <groeck@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>