drm/probe_helper: extract two helper functions

Extract drm_kms_helper_enable_hpd() and drm_kms_helper_disable_hpd(),
two helpers that enable and disable HPD handling on all device's
connectors.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230124104548.3234554-1-dmitry.baryshkov@linaro.org