drm/i915: don't disable fdi links harder in ilk_crtc_enable

Because they should have been disabled when shutting down the display
pipe previously. To ensure that this is the case, add a few assserts
instead of unconditionally disabling the fdi link.
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -3184,10 +3184,12 @@ static void ironlake_crtc_enable(struct drm_crtc *crtc)
 
 	is_pch_port = intel_crtc_driving_pch(crtc);
 
-	if (is_pch_port)
+	if (is_pch_port) {
 		ironlake_fdi_pll_enable(intel_crtc);
-	else
-		ironlake_fdi_disable(crtc);
+	} else {
+		assert_fdi_tx_disabled(dev_priv, pipe);
+		assert_fdi_rx_disabled(dev_priv, pipe);
+	}
 
 	for_each_encoder_on_crtc(dev, crtc, encoder)
 		if (encoder->pre_enable)