Enable intra_y_mode_mask pruning for real time enc

Following my previous CL
https://aomedia-review.googlesource.com/c/aom/+/138781
this CL enabled using intra_y_mode_mask to prune intra
mode search for real time encoding. This gave huge encoder
speedup for speed 5 & 6 without much quality loss.
Borg test result:
             avg_psnr:  ovr_psnr:  ssim:
rtc speed 5
rtc_derf:     0.243     0.385      0.351
rtc speed 6
rtc_derf:     0.434     0.548      0.564

Average encoder speedup over 5 clips are 44.7% for speed 5
and 42.2% for speed 6.

STATS_CHANGED

Change-Id: I01818a80c6e1d260bcad01587837c6f83faddca7

av1/encoder/speed_features.c

diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index eef1e24..3aeb9cc 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -1356,9 +1356,7 @@
     sf->inter_sf.inter_mode_rd_model_estimation = 2;
 
     for (int i = 0; i < TX_SIZES; ++i) {
-      // TODO(yunqing): comment this out to keep rt performance unchanged. Will
-      // explore it further.
-      // sf->intra_sf.intra_y_mode_mask[i] = INTRA_DC;
+      sf->intra_sf.intra_y_mode_mask[i] = INTRA_DC;
       sf->intra_sf.intra_uv_mode_mask[i] = UV_INTRA_DC_CFL;
     }
 
@@ -1408,6 +1406,12 @@
 
     sf->inter_sf.inter_mode_rd_model_estimation = 2;
 
+    // Disable intra_y_mode_mask pruning since the performance at speed 7 isn't
+    // good. May need more study.
+    for (int i = 0; i < TX_SIZES; ++i) {
+      sf->intra_sf.intra_y_mode_mask[i] = INTRA_ALL;
+    }
+
     sf->lpf_sf.lpf_pick = LPF_PICK_FROM_Q;
 
     sf->rt_sf.mode_search_skip_flags |= FLAG_SKIP_INTRA_DIRMISMATCH;

test/rt_end_to_end_test.cc

diff --git a/test/rt_end_to_end_test.cc b/test/rt_end_to_end_test.cc
index 8590f80..9997339 100644
--- a/test/rt_end_to_end_test.cc
+++ b/test/rt_end_to_end_test.cc
@@ -44,7 +44,7 @@
                            { 8, { { 0, 36.0 }, { 3, 36.5 } } },
                            { 9, { { 0, 35.5 }, { 3, 36.1 } } } } },
                        { "niklas_1280_720_30.y4m",
-                         { { 5, { { 0, 34.4 }, { 3, 34.4 } } },
+                         { { 5, { { 0, 34.4 }, { 3, 34.32 } } },
                            { 6, { { 0, 34.2 }, { 3, 34.2 } } },
                            { 7, { { 0, 33.6 }, { 3, 33.6 } } },
                            { 8, { { 0, 33.48 }, { 3, 33.48 } } },