Simplify the mode_info size logic

Replace the arithmetic calculation with direct table access.

Change-Id: I054a4c398f2321a39330aaf00607dc180a335b2d

av1/decoder/decodeframe.c

@@ -1362,8 +1362,8 @@ static void decode_block(AV1Decoder *const pbi, MACROBLOCKD *const xd,
 #endif  // CONFIG_EXT_PARTITION_TYPES
                          BLOCK_SIZE bsize, int bwl, int bhl) {
   AV1_COMMON *const cm = &pbi->common;
-  const int bw = 1 << (bwl - 1);
-  const int bh = 1 << (bhl - 1);
+  const int bw = mi_size_wide[bsize];
+  const int bh = mi_size_high[bsize];
   const int x_mis = AOMMIN(bw, cm->mi_cols - mi_col);
   const int y_mis = AOMMIN(bh, cm->mi_rows - mi_row);
   MB_MODE_INFO *mbmi;

av1/decoder/decodemv.c

@@ -770,8 +770,8 @@ static void read_intra_frame_mode_info(AV1_COMMON *const cm,
   const BLOCK_SIZE bsize = mbmi->sb_type;
   int i;
   const int mi_offset = mi_row * cm->mi_cols + mi_col;
-  const int bw = xd->plane[0].n4_w >> 1;
-  const int bh = xd->plane[0].n4_h >> 1;
+  const int bw = mi_size_wide[bsize];
+  const int bh = mi_size_high[bsize];
 
   // TODO(slavarnway): move x_mis, y_mis into xd ?????
   const int x_mis = AOMMIN(cm->mi_cols - mi_col, bw);