drm/i915: Fake HDMI live status

This patch does the following:
- Fakes live status of HDMI as connected (even if that's not).
  While testing certain (monitor + cable) combinations with
  various intel  platforms, it seems that live status register
  doesn't work reliably on some older devices. So limit the
  live_status check for HDMI detection, only for platforms
  from gen7 onwards.

V2: restrict faking live_status to certain platforms
V3: (Ville)
   - keep the debug message for !live_status case
   - fix indentation of comment
   - remove "warning" from the debug message

    (Jani)
   - Change format of fix details in the commit message

Fixes: 237ed86c ("drm/i915: Check live status before reading edid")
Cc: stable@vger.kernel.org # v4.4
Suggested-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461237606-16491-1-git-send-email-shashank.sharma@intel.com


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>