drm/i915: Implement chv display PHY lane stagger setup

Set up the chv display PHY lane stagger registers according to
"Programming Guide for 1273 CHV eDP/DP/HDMI Display PHY" v1.04

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>