Enable CWG-E135 speedup tool for A3.

Speedup: 35% RA, 28% LD
BDrate loss: 0.05%

av1/encoder/speed_features.c

diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index 2f453aa..8ce9dd4 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -1008,8 +1008,10 @@
         sf->part_sf.prune_split_ml_level = 3;
       } else if (is_1080p_or_larger) {
         sf->part_sf.prune_split_ml_level = 2;
+      } else if (is_720p_or_larger) {
+        sf->part_sf.prune_split_ml_level = 0;
       } else {
-        // Not pruning in anything lower than A2
+        // No pruning for resolutions lower than 720p
         sf->part_sf.prune_split_with_ml = 0;
       }
 #endif  // CONFIG_ML_PART_SPLIT