drm/probe-helper: enable and disable HPD on connectors

Introduce two drm_connector_helper_funcs: enable_hpd() and disable_hpd().
They are called by drm_kms_helper_poll_enable() and
drm_kms_helper_poll_disable() (and thus drm_kms_helper_poll_init() and
drm_kms_helper_poll_fini()) respectively.

This allows DRM drivers to rely on drm_kms_helper_poll for enabling and
disabling HPD detection rather than doing that manually.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221102180705.459294-3-dmitry.baryshkov@linaro.org