move segmentation_common to encoder

vp8_update_gf_useage_maps() is only used by the encoder. This patch
fixes the ability to build in decode-only or encode-only
configurations.

Change-Id: I3a5211428e539886ba998e09e8abd747ac55c9aa

vp8/encoder/segmentation.h

@@ -0,0 +1,16 @@
+/*
+ *  Copyright (c) 2010 The VP8 project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+
+#include "string.h"
+#include "blockd.h"
+#include "onyx_int.h"
+
+extern void vp8_update_gf_useage_maps(VP8_COMP *cpi, VP8_COMMON *cm, MACROBLOCK *x);