drm/i915: Nuke debug messages from the pipe update critical section

printks are slow so we should not be doing them from the vblank evade
critical section. These could explain why we sometimes seem to
blow past our 100 usec deadline.

The problem has been there ever since commit bfd16b2a ("drm/i915:
Make updating pipe without modeset atomic.") but it may not have
been readily visible until commit e1edbd44 ("drm/i915: Complain
if we take too long under vblank evasion.") increased our chances
of noticing it.

Cc: stable@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: bfd16b2a

 ("drm/i915: Make updating pipe without modeset atomic.")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170307205419.19447-1-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>