drm/i915: Disable all infoframes when turning off the HDMI port

Currently we just disable the GCP infoframe when turning off the port.
That means if the same transcoder is used on a DP port next, we might
end up pushing infoframes over DP, which isn't intended. Just disable
all the infoframes when turning off the port.

Also protect against two ports stomping on each other on g4x due to
the single video DIP instance. Now only the first port to enable
gets to send infoframes.

v2: Rebase

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chandra Konduru <Chandra.konduru@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>