drm/i915: Disable trickle feed for SNB/IVB cursors

We disable trickle feed whenever possible, except for the cursors
on SNB/IVB. Let's try disabling it there too if for no other reason
than consistency.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130203807.13721-5-ville.syrjala@linux.intel.comReviewed-by: Mika Kahola <mika.kahola@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -9711,6 +9711,9 @@ static u32 i9xx_cursor_ctl(const struct intel_crtc_state *crtc_state,
 	struct intel_crtc *crtc = to_intel_crtc(crtc_state->base.crtc);
 	u32 cntl = 0;
 
+	if (IS_GEN6(dev_priv) || IS_IVYBRIDGE(dev_priv))
+		cntl |= MCURSOR_TRICKLE_FEED_DISABLE;
+
 	if (INTEL_GEN(dev_priv) <= 10) {
 		cntl |= MCURSOR_GAMMA_ENABLE;