drm/i915: disable temporal dithering on the internal panel

<ajax> i'm getting tempted to just disable temporal
<mjg59> Approved.
<ajax> apparently it makes the screen look pulse-y which is worse
than the disease.

References: http://lists.freedesktop.org/archives/intel-gfx/2011-October/012545.html
Tested-by: Олег Герман <oleg.german@gmail.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_display.c

@@ -5671,7 +5671,7 @@ static int ironlake_crtc_mode_set(struct drm_crtc *crtc,
 	pipeconf &= ~PIPECONF_DITHER_TYPE_MASK;
 	if ((is_lvds && dev_priv->lvds_dither) || dither) {
 		pipeconf |= PIPECONF_DITHER_EN;
-		pipeconf |= PIPECONF_DITHER_TYPE_ST1;
+		pipeconf |= PIPECONF_DITHER_TYPE_SP;
 	}
 	if (is_dp || intel_encoder_is_pch_edp(&has_edp_encoder->base)) {
 		intel_dp_set_m_n(crtc, mode, adjusted_mode);