drm/i915: make SDVO TV-out work for multifunction devices

We need to track this correctly. While at it shovel the boolean
to track whether the sdvo is in tv mode or not into pipe_config.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=36997
Tested-by: Pierre Assal <pierre.assal@verint.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=63609
Tested-by: cancan,feng <cancan.feng@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>