Add 2x2 block unit syntax

Add 2x2 block size syntax to the codec system. It prepares for the
4x4 coding block unit for 420 format. This change retains the same
coding statistics.

Change-Id: If8e9a31bd6b4b75bc994539dc4dd8021d455ba57
diff --git a/av1/encoder/encodeframe.c b/av1/encoder/encodeframe.c
index 50199b9..b0636d5 100644
--- a/av1/encoder/encodeframe.c
+++ b/av1/encoder/encodeframe.c
@@ -2928,6 +2928,9 @@
 
 /* clang-format off */
 static const BLOCK_SIZE min_partition_size[BLOCK_SIZES] = {
+#if CONFIG_CB4X4
+  BLOCK_2X2,   BLOCK_2X2,   BLOCK_2X2,    //    2x2,    2x4,     4x2
+#endif
                             BLOCK_4X4,    //                     4x4
   BLOCK_4X4,   BLOCK_4X4,   BLOCK_4X4,    //    4x8,    8x4,     8x8
   BLOCK_4X4,   BLOCK_4X4,   BLOCK_8X8,    //   8x16,   16x8,   16x16
@@ -2939,6 +2942,9 @@
 };
 
 static const BLOCK_SIZE max_partition_size[BLOCK_SIZES] = {
+#if CONFIG_CB4X4
+  BLOCK_4X4,     BLOCK_4X4,       BLOCK_4X4,    //    2x2,    2x4,     4x2
+#endif
                                   BLOCK_8X8,    //                     4x4
   BLOCK_16X16,   BLOCK_16X16,   BLOCK_16X16,    //    4x8,    8x4,     8x8
   BLOCK_32X32,   BLOCK_32X32,   BLOCK_32X32,    //   8x16,   16x8,   16x16
@@ -2951,6 +2957,9 @@
 
 // Next square block size less or equal than current block size.
 static const BLOCK_SIZE next_square_size[BLOCK_SIZES] = {
+#if CONFIG_CB4X4
+  BLOCK_2X2,   BLOCK_2X2,     BLOCK_2X2,    //    2x2,    2x4,     4x2
+#endif
                               BLOCK_4X4,    //                     4x4
   BLOCK_4X4,   BLOCK_4X4,     BLOCK_8X8,    //    4x8,    8x4,     8x8
   BLOCK_8X8,   BLOCK_8X8,     BLOCK_16X16,  //   8x16,   16x8,   16x16