Add encoder speed 6

The goal is to provide a really fast speed setting, and meet fast
encoding needs.

Change-Id: If32e06fb03f81428e69386f6d71788e22bddd0ee
diff --git a/apps/aomenc.c b/apps/aomenc.c
index a687050..4e15683 100644
--- a/apps/aomenc.c
+++ b/apps/aomenc.c
@@ -405,7 +405,7 @@
 #if CONFIG_AV1_ENCODER
 static const arg_def_t cpu_used_av1 =
     ARG_DEF(NULL, "cpu-used", 1,
-            "Speed setting (0..5 in good mode, 6..8 in realtime mode)");
+            "Speed setting (0..6 in good mode, 6..8 in realtime mode)");
 static const arg_def_t rowmtarg =
     ARG_DEF(NULL, "row-mt", 1,
             "Enable row based multi-threading (0: off, 1: on (default))");
diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index 0e2e55a..345cdfc 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -594,6 +594,9 @@
     sf->mv_sf.prune_mesh_search = 1;
     sf->mv_sf.reduce_search_range = 1;
   }
+
+  if (speed >= 6) {
+  }
 }
 
 // TODO(kyslov): now this is very similar to