drm/i915: expose HDMI connectors on port C on BYT

Ryan noticed that on his board, HDMI was wired up to port C but not
exposed by the kernel, which had only expected DP on that port.  Fix
that up by enumerating both ports if possible.

Tested-by: "Matsumura, Ryan" <ryan.matsumura@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: Fix up the whitespace fail. Tsk.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>