AV1 RT: Limit max BSize for Intra mode search

This have almost no impact on quality, but brings back 10% of speed

Change-Id: Id26f6817b605a958721eee0326efd335d8d60ae6
diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index b593121..54b870a 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -614,6 +614,7 @@
     sf->use_comp_ref_nonrd = 0;
     sf->inter_mode_rd_model_estimation = 2;
     sf->cdef_pick_method = CDEF_PICK_FROM_Q;
+    sf->max_intra_bsize = BLOCK_16X16;
   }
   if (speed >= 8) {
     sf->use_fast_nonrd_pick_mode = 1;