Disable extended partitions on speed 6

Performance:
 TESTSET | AVG_PSNR | OVR_PSNR |   SSIM  |  SPD
---------+----------+----------+---------+-------
   HDRES |  +0.092% |  +0.099% | +0.152% | +0.8%
  MIDRES |  +0.004% |  +0.004% | +0.006% | +0.0%
  LOWRES |  +0.007% |  +0.002% | +0.002% | +0.0%

STATS_CHANGED

Change-Id: Id2bb4ec0e05b468d02224d2c6fe111d5d54f3fb1

av1/encoder/speed_features.c

diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index f4a646d..481b86d 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -1089,7 +1089,7 @@
     sf->part_sf.prune_sub_8x8_partition_level =
         allow_screen_content_tools ? 0
                                    : frame_is_intra_only(&cpi->common) ? 1 : 2;
-    sf->part_sf.prune_part4_search = 3;
+    sf->part_sf.ext_partition_eval_thresh = BLOCK_128X128;
 
     sf->mv_sf.simple_motion_subpel_force_stop = FULL_PEL;
     sf->mv_sf.use_bsize_dependent_search_method = 1;

av1/encoder/speed_features.h

diff --git a/av1/encoder/speed_features.h b/av1/encoder/speed_features.h
index 21c510d..04b681f 100644
--- a/av1/encoder/speed_features.h
+++ b/av1/encoder/speed_features.h
@@ -438,7 +438,8 @@
   // Used if partition_search_type = FIXED_PARTITION
   BLOCK_SIZE fixed_partition_size;
 
-  // Prune extended partition types search
+  // Prune extended partition types search based on the current partition type
+  // and the rdcost found in the subblocks.
   // Can take values 0 - 2, 0 referring to no pruning, and 1 - 2 increasing
   // aggressiveness of pruning in order.
   int prune_ext_partition_types_search_level;
@@ -523,10 +524,12 @@
   // perform split/no_split decision on intra-frames.
   int intra_cnn_split;
 
-  // Disable extended partition search for lower block sizes.
-  int ext_partition_eval_thresh;
+  // Disable extended partition search if the current bsize is greater than the
+  // threshold.
+  BLOCK_SIZE ext_partition_eval_thresh;
 
-  // prune extended partition search
+  // Prune extended partition search based on whether the split/rect partitions
+  // provided an improvement in the previous search.
   // 0 : no pruning
   // 1 : prune 1:4 partition search using winner info from split partitions
   // 2 : prune 1:4 and AB partition search using split and HORZ/VERT info