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

drm/i915: Nuke skl_update_plane debug message 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 c331879ce8ea ("drm/i915:
skylake sprite plane scaling using shared scalers.") but it may not have
been readily visible until commit e1edbd44e23b ("drm/i915: Complain
if we take too long under vblank evasion.") increased our chances
of noticing it.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1488974407-25175-1-git-send-email-maarten.lankhorst@linux.intel.com
Fixes: c331879ce8ea ("drm/i915: skylake sprite plane scaling using shared scalers")
Cc: <stable@vger.kernel.org> # v4.2+
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[mlankhorst: Add missing tags, point to the correct offending commit]