If an hotplug event only updates a single connector, use
drm_kms_helper_connector_hotplug_event instead of
drm_kms_helper_hotplug_event.

Changes in v4:
- Simplify loop logic (Ville, Sam)
- Update drm_connector_helper_hpd_irq_event (Maxime)
Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211018084707.32253-6-contact@emersion.fr