drm/i915: Clean up early plane debugs

Print the plane hw state readout results in the common format
we already use for pipes and encoders. Also print some clearer
debug messages when we disable planes during the early phases
of state readout/sanitization.

v2: Rebase

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181003145052.4633-1-ville.syrjala@linux.intel.com


Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>