decodemv.h: add av1_neg_deinterleave prototype

+ include decodemv.h and bitstream.h in segment_binarization_sync.cc to
  avoid duplicating the declarations

Fixes a -Wmissing-prototypes warning:

av1/decoder/decodemv.c|257 col 5| warning: no previous prototype for
  ‘av1_neg_deinterleave’ [-Wmissing-prototypes]
   257 | int av1_neg_deinterleave(int diff, int ref, int max) {
       |     ^~~~~~~~~~~~~~~~~~~~

Bug: aomedia:3416
Change-Id: I56214ef582d1549b7974a3c812b155a4a49a991c

av1/decoder/decodemv.h

diff --git a/av1/decoder/decodemv.h b/av1/decoder/decodemv.h
index 3d8629c..7e77c03 100644
--- a/av1/decoder/decodemv.h
+++ b/av1/decoder/decodemv.h
@@ -20,6 +20,8 @@
 extern "C" {
 #endif
 
+int av1_neg_deinterleave(int diff, int ref, int max);
+
 void av1_read_mode_info(AV1Decoder *const pbi, DecoderCodingBlock *dcb,
                         aom_reader *r, int x_mis, int y_mis);
 

test/segment_binarization_sync.cc

diff --git a/test/segment_binarization_sync.cc b/test/segment_binarization_sync.cc
index bd8cf11..108e66a 100644
--- a/test/segment_binarization_sync.cc
+++ b/test/segment_binarization_sync.cc
@@ -10,15 +10,14 @@
  */
 
 #include "third_party/googletest/src/googletest/include/gtest/gtest.h"
+
+#include "av1/common/seg_common.h"
+#include "av1/decoder/decodemv.h"
+#include "av1/encoder/bitstream.h"
 #include "test/acm_random.h"
 
 using libaom_test::ACMRandom;
 
-extern "C" {
-int av1_neg_interleave(int x, int ref, int max);
-int av1_neg_deinterleave(int diff, int ref, int max);
-}
-
 namespace {
 
 struct Segment {
@@ -28,8 +27,6 @@
 };
 
 Segment GenerateSegment(int seed) {
-  static const int MAX_SEGMENTS = 8;
-
   ACMRandom rnd_(seed);
 
   Segment segment;