drm/edid: respect connector force for drm_get_edid ddc probe

Skip DDC probe for forced connector status. Don't try to read the EDID
if the connector is forced off. Skipping probe for forced on connectors
will make more sense when drm_do_get_edid() will handle override and
firmware EDIDs.

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487344854-18777-4-git-send-email-jani.nikula@intel.com