drm/i915: Mark all HPD capabled connectors as such

Currently we only set the DRM_CONNECTOR_POLL_{DISCONNECT,CONNECT}
bits in intel_connector->polled (the base setting), leading to
some confusing looking code to reset drm_connector->polled
(the actual setting) to DRM_CONNECTOR_POLL_HPD. Let's set
intel_connector->polled = DRM_CONNECTOR_POLL_HPD for all hpd
capable connectors, and then we don't need so many special
cases in the hotplug code.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200205183546.9291-3-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>