drm/i915: Allow DP to work w/o EDID

Allow returning "connected" or "unknown" connector status for DP branch
devices that don't have an EDID. Currently we'd claim the thing as
"disconnected" if there is no EDID.

This stuff used to broken already, I think, but it got more broken by
commit f21a2198 ("drm/i915: Splitting intel_dp_detect")

Cc: Damien Cassou <damien@cassou.me>
Cc: freedesktop.org@gp.mailgun.org
Cc: Arno <blouin.arno@gmail.com>
Cc: Shubhangi Shrivastava <shubhangi.shrivastava@intel.com>
Cc: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Cc: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Cc: stable@vger.kernel.org
Tested-by: Arno <blouin.arno@gmail.com>
Fixes: f21a2198 ("drm/i915: Splitting intel_dp_detect")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=83348


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475481316-8194-2-git-send-email-ville.syrjala@linux.intel.com


Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
(cherry picked from commit 5cb651a7)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>