Set use_sqr_partition_only_thresh on hdres speed 2

On speed 2, sets use_square_partition_only_threshold to BLOCK_64X64 on
hdres.

Performance Evaluation:

        | HDRES |
AVG_PSNR|-0.007%|
OVR_PSNR| 0.000%|
TIME_RDX| 1.599%|

STATS_CHANGED

Change-Id: If412b849fa3857ebeb3a28f0b02cdc9be80a32db
diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index 67678f0..ae3f161 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -131,11 +131,16 @@
 
   if (speed >= 2) {
     if (is_720p_or_larger) {
-      // TODO(chiyotsai@google.com): Set a threshold for hdres
-      sf->use_square_partition_only_threshold = BLOCK_128X128;
+      sf->use_square_partition_only_threshold = BLOCK_64X64;
     } else if (is_480p_or_larger) {
       sf->use_square_partition_only_threshold = BLOCK_32X32;
+    } else {
+      // TODO(chiyotsai@google.com): Setting the threshold to BLOCK_16X16 incurs
+      // a large loss (about 0.584%). Try increasing the threshold on boosted
+      // frame and see if it improves the performance.
+      sf->use_square_partition_only_threshold = BLOCK_32X32;
     }
+
     if (is_720p_or_larger) {
       sf->disable_split_mask =
           cm->show_frame ? DISABLE_ALL_SPLIT : DISABLE_ALL_INTER_SPLIT;