Use the chessboard pattern pred search in newmv mode

This commit extends the chessboard pattern prediction filter search.
If the above and left blocks have the same prediction filter type,
the encoder will skip the prediction filter type search and use the
reference one.

The overall chessboard pattern prediction filter type search reduces
speed 3 runtime for hard clips. Experiments on park joy at 1080p
and 15000 kbps show that the runtime goes from 723265 ms to 65832 ms,
i.e., about 10% speed-up. Compression performance wise, it affects
the coding quality by

Change-Id: I880975497c7ad166532e9eea9bf46684d77ff327
derf:    -0.326%
yt:      -0.257%
hd:      -0.241%
stdhd:   -0.417%

vp9/encoder/vp9_rdopt.c

diff --git a/vp9/encoder/vp9_rdopt.c b/vp9/encoder/vp9_rdopt.c
index ef81959..e5d0e6a 100644
--- a/vp9/encoder/vp9_rdopt.c
+++ b/vp9/encoder/vp9_rdopt.c
@@ -2045,11 +2045,15 @@
   int pred_filter_search = cpi->sf.cb_pred_filter_search ?
       (((mi_row + mi_col) >> bsl)) & 0x01 : 0;
 
-  if (pred_filter_search && this_mode != NEWMV) {
+  if (pred_filter_search) {
+    INTERP_FILTER af = SWITCHABLE, lf = SWITCHABLE;
     if (xd->up_available)
-      best_filter = xd->mi[-xd->mi_stride]->mbmi.interp_filter;
-    else if (xd->left_available)
-      best_filter = xd->mi[-1]->mbmi.interp_filter;
+      af = xd->mi[-xd->mi_stride]->mbmi.interp_filter;
+    if (xd->left_available)
+      lf = xd->mi[-1]->mbmi.interp_filter;
+
+    if ((this_mode != NEWMV) || (af == lf))
+      best_filter = af;
   }
 
   if (is_comp_pred) {