drm/i915/fbc: Don't clear busy_bits for origin==GTT

The hardware host tracking won't nuke the entire cfb (unless the
entire fb is written through the gtt) so don't clear the busy_bits
for gtt tracking.

Not that it really matters anymore since we've lost ORIGIN_GTT usage
everywhere.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429101034.8208-7-ville.syrjala@linux.intel.comReviewed-by: José Roberto de Souza <jose.souza@intel.com>

drivers/gpu/drm/i915/display/intel_fbc.c

@@ -1078,11 +1078,19 @@ void intel_fbc_flush(struct drm_i915_private *dev_priv,
 	if (!HAS_FBC(dev_priv))
 		return;
 
+	/*
+	 * GTT tracking does not nuke the entire cfb
+	 * so don't clear busy_bits set for some other
+	 * reason.
+	 */
+	if (origin == ORIGIN_GTT)
+		return;
+
 	mutex_lock(&fbc->lock);
 
 	fbc->busy_bits &= ~frontbuffer_bits;
 
-	if (origin == ORIGIN_GTT || origin == ORIGIN_FLIP)
+	if (origin == ORIGIN_FLIP)
 		goto out;
 
 	if (!fbc->busy_bits && fbc->crtc &&