drm/i915: Unbreak check_digital_port_conflicts()

Atomic changes broke check_digital_port_conflicts(). It needs to look
at the global situation instead of just trying to find a conflict
within the current atomic state.

This bug made my HSW explode spectacularly after I had split the DDI
encoders into separate DP and HDMI encoders. With the fix, things
seem much more solid.

I hope holding the connection_mutex is enough protection that we can
actually walk the connectors even if they're not part of the current
atomic state...

v2: Regenerate the patch so that it actually applies (Jani)

Cc: stable@vger.kernel.org
Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Fixes: 5448a00d

 ("drm/i915: Don't use staged config in check_digital_port_conflicts()")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449764551-12466-1-git-send-email-ville.syrjala@linux.intel.com
(cherry picked from commit 0bff4858

)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>