Explicitly use block size to determine partition info

Replace the use of num_4x4_log2 with the actual block size as the
condition to check if a block is partitionable. This avoids conflict
issues when multiple experiments are turned on.

Change-Id: I666d52458590a6f88c3995a140d20b0d66d27bfb

av1/decoder/decodeframe.c

@@ -2061,9 +2061,9 @@ static void decode_partition(AV1Decoder *const pbi, MACROBLOCKD *const xd,
 
   if (mi_row >= cm->mi_rows || mi_col >= cm->mi_cols) return;
 
-  partition = (n4x4_l2 == 0) ? PARTITION_NONE
-                             : read_partition(cm, xd, mi_row, mi_col, r,
-                                              has_rows, has_cols, bsize);
+  partition = (bsize < BLOCK_8X8) ? PARTITION_NONE
+                                  : read_partition(cm, xd, mi_row, mi_col, r,
+                                                   has_rows, has_cols, bsize);
   subsize = subsize_lookup[partition][bsize];  // get_subsize(bsize, partition);
 
 #if CONFIG_PVQ