Refactor tx_size step use cases in decoder

Use lookup table to replace the arithmetic computation for transform
block step.

Change-Id: Ie7cb33e75e3b90aa9e9b46f8d11fa1d03e1ebe85

av1/decoder/decodeframe.c

@@ -507,7 +507,7 @@ static void decode_block(AV1Decoder *const pbi, MACROBLOCKD *const xd,
                 : mbmi->tx_size;
       const int num_4x4_w = pd->n4_w;
       const int num_4x4_h = pd->n4_h;
-      const int step = (1 << tx_size);
+      const int step = tx_size_1d_in_unit[tx_size];
       int row, col;
       const int max_blocks_wide =
           num_4x4_w + (xd->mb_to_right_edge >= 0
@@ -542,7 +542,7 @@ static void decode_block(AV1Decoder *const pbi, MACROBLOCKD *const xd,
                   : mbmi->tx_size;
         const int num_4x4_w = pd->n4_w;
         const int num_4x4_h = pd->n4_h;
-        const int step = (1 << tx_size);
+        const int step = tx_size_1d_in_unit[tx_size];
         int row, col;
         const int max_blocks_wide =
             num_4x4_w + (xd->mb_to_right_edge >= 0

av1/decoder/detokenize.c

@@ -57,7 +57,7 @@ static int decode_coefs(const MACROBLOCKD *xd, PLANE_TYPE type,
 #endif
 {
   FRAME_COUNTS *counts = xd->counts;
-  const int max_eob = 16 << (tx_size << 1);
+  const int max_eob = 1 << (tx_size_1d_log2[tx_size] * 2);
   const FRAME_CONTEXT *const fc = xd->fc;
   const int ref = is_inter_block(&xd->mi[0]->mbmi);
 #if CONFIG_AOM_QM