Add unittest for encoder row based multi-threading

Added row-mt/row_mt as a command-line/init-time API parameter
in the encoder. Currently, encoding with row-mt=1 has only tile
level multi-threading. Support for row level multi-threading of
the encoding stage will be added eventually.

Change-Id: I67450dda05d1a1c32131d0998dd6546e147b681d
diff --git a/apps/aomenc.c b/apps/aomenc.c
index 7abed80..7518e3a 100644
--- a/apps/aomenc.c
+++ b/apps/aomenc.c
@@ -414,6 +414,9 @@
 static const arg_def_t single_tile_decoding =
     ARG_DEF(NULL, "single-tile-decoding", 1,
             "Single tile decoding (0: off (default), 1: on)");
+static const arg_def_t rowmtarg =
+    ARG_DEF(NULL, "row-mt", 1,
+            "Enable row based multi-threading (0: off (default), 1: on)");
 static const arg_def_t tile_cols =
     ARG_DEF(NULL, "tile-columns", 1, "Number of tile columns to use, log2");
 static const arg_def_t tile_rows =
@@ -621,6 +624,7 @@
                                        &sharpness,
                                        &static_thresh,
                                        &single_tile_decoding,
+                                       &rowmtarg,
                                        &tile_cols,
                                        &tile_rows,
                                        &arnr_maxframes,
@@ -676,6 +680,7 @@
                                         AOME_SET_SHARPNESS,
                                         AOME_SET_STATIC_THRESHOLD,
                                         AV1E_SET_SINGLE_TILE_DECODING,
+                                        AV1E_SET_ROW_MT,
                                         AV1E_SET_TILE_COLUMNS,
                                         AV1E_SET_TILE_ROWS,
                                         AOME_SET_ARNR_MAXFRAMES,