Disable first pass partition search on speed >= 4

On speed 4 and above, use_square_only_threshold is set to BLOCK_4X4 on
non-boosted frames, so the behavior of first partition search and second
partition search are almost identical. Disabling
first_partition_search_pass thus gives significant speed up.

Performance:
 AVG_PSNR | OVR_PSNR |   SSIM   | AVG_SPD_UP | SPD_UP:AVG_PSNR
 +0.1401% | +0.1385% | +0.3294% |  +16.259%  |    116:1

STATS_CHANGED

Change-Id: I5368356627f7b9ed0b4f4abf9379d15cab8b1df2

av1/encoder/speed_features.c

diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index 614f329..5e9eda3 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -241,7 +241,8 @@
     sf->inter_tx_size_search_init_depth_sqr = 1;
     sf->intra_tx_size_search_init_depth_rect = 1;
     sf->tx_size_search_lgr_block = 1;
-    if (speed >= CONFIG_2PASS_PARTITION_SEARCH_LVL) {
+    if (speed >= CONFIG_2PASS_PARTITION_SEARCH_LVL_START &&
+        speed < CONFIG_2PASS_PARTITION_SEARCH_LVL_END) {
       sf->two_pass_partition_search = 1;
       sf->mode_pruning_based_on_two_pass_partition_search = 1;
     }

build/cmake/aom_config_defaults.cmake

diff --git a/build/cmake/aom_config_defaults.cmake b/build/cmake/aom_config_defaults.cmake
index 47aba55..b1c835c 100644
--- a/build/cmake/aom_config_defaults.cmake
+++ b/build/cmake/aom_config_defaults.cmake
@@ -123,7 +123,9 @@
 set_aom_config_var(CONFIG_FP_MB_STATS 0 NUMBER "AV1 experiment flag.")
 set_aom_config_var(CONFIG_INTER_STATS_ONLY 0 NUMBER "AV1 experiment flag.")
 set_aom_config_var(CONFIG_RD_DEBUG 0 NUMBER "AV1 experiment flag.")
-set_aom_config_var(CONFIG_2PASS_PARTITION_SEARCH_LVL 1 NUMBER
+set_aom_config_var(CONFIG_2PASS_PARTITION_SEARCH_LVL_START 1 NUMBER
+                   "AV1 experiment flag.")
+set_aom_config_var(CONFIG_2PASS_PARTITION_SEARCH_LVL_END 4 NUMBER
                    "AV1 experiment flag.")
 set_aom_config_var(CONFIG_SHARP_SETTINGS 0 NUMBER "AV1 experiment flag.")
 set_aom_config_var(CONFIG_ONE_PASS_SVM 0 NUMBER "AV1 experiment flag.")