drm/i915: Improve PCBR debug information

Always print the final PCBR register value on both vlv and chv, and
also tell us whether the BIOS was a good citizen or not.

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