drm/i915: only set the HDMI port on the DIP once

Not once for each InfoFrame. Now we have a function that allows us to
do this.

[danvet: Paulo clarified on irc that a later bugfix patch needs this
cleanup.]

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>