drm/i915: Remove debug prints from primary plane update funcs

These are now called from the plane commit hooks, so they really need to
be fast or else we risk atomic update failures. So kill the debug prints
which are slowing things down massively.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>