Add MV refining search in warped motion experiment

Implemented a MV refining search after the warped motion parameters were
found. Only 4 or 8 positions were checked so there was almost no impact
on encoder speed.

Borg test result:
            avg_psnr     ovr_psnr    ssim
cam_lowres: -0.543%      -0.574%     -0.670%
lowres    : -0.222%      -0.230%     -0.285%

Change-Id: Ic2f6c1fe548b089d50e9c33bb365e6b128aabc93
diff --git a/av1/encoder/mcomp.h b/av1/encoder/mcomp.h
index 9ed0817..7e8b4b2 100644
--- a/av1/encoder/mcomp.h
+++ b/av1/encoder/mcomp.h
@@ -153,4 +153,14 @@
 }  // extern "C"
 #endif
 
+#if CONFIG_WARPED_MOTION
+unsigned int av1_compute_motion_cost(const struct AV1_COMP *cpi,
+                                     MACROBLOCK *const x, BLOCK_SIZE bsize,
+                                     int mi_row, int mi_col, const MV *this_mv);
+unsigned int av1_refine_warped_mv(const struct AV1_COMP *cpi,
+                                  MACROBLOCK *const x, BLOCK_SIZE bsize,
+                                  int mi_row, int mi_col, int *pts,
+                                  int *pts_inref);
+#endif  // CONFIG_WARPED_MOTION
+
 #endif  // AV1_ENCODER_MCOMP_H_