drm/i915: Kill intel_dp->{link_bw, rate_select}

We only need the link_bw/rate_select parameters when starting link
training, and they should be computed based on the currently active
config, so throw them out from intel_dp and just compute on demand.

Toss in an extra debug print to see rate_select in addition to link_bw,
as the latter may be 0 for eDP 1.4.

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>