drm/i915: Move intel_dp->lane_count into pipe_config

Currently we clobber intel_dp->lane_count in compute config, which means
after a rejected modeset we may no longer be able to retrain the current
link. Move lane_count into pipe_config to avoid that.

v2: Add missing ':' to the pipe config debug dump

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>