Put iterative motion search under speed control

Enable iterative motion search for compound inter-inter prediction
of block sizes 4x4/4x8/8x4 only when best coding quality is selected.
The iterative motion search provides about 0.1% gains for derf and
stdhd at this point, at the expense of longer runtime.

Change-Id: Idc03e7f827e51f1bb8d269bc3752ee297a6bbfe5

vp9/encoder/vp9_rdopt.c

diff --git a/vp9/encoder/vp9_rdopt.c b/vp9/encoder/vp9_rdopt.c
index 6a6473a..211a265 100644
--- a/vp9/encoder/vp9_rdopt.c
+++ b/vp9/encoder/vp9_rdopt.c
@@ -1379,7 +1379,7 @@
 
           // adjust src pointers
           mi_buf_shift(x, i);
-          if (cpi->sf.comp_inter_joint_search) {
+          if (cpi->compressor_speed == 0 && cpi->sf.comp_inter_joint_search) {
             iterative_motion_search(cpi, x, bsize, frame_mv[this_mode],
                                     scaled_ref_frame,
                                     mi_row, mi_col, seg_mvs[i]);