Reduce dqcoeff array size in decoder

The decoding process handles detokenization and reconstruction per
transform block sequentially. There is no need to offset the dqcoeff
buffer according to the transform block index. This allows to
reduce the memory spill and improve cache performance.

Change-Id: Ibb8bfe532a7a08fcabaf6d42cbec1e986901d32d

vp9/decoder/vp9_detokenize.c

@@ -217,7 +217,7 @@ int vp9_decode_block_tokens(MACROBLOCKD *xd,
                                                pd->left_context + y);
   const scan_order *so = get_scan(xd, tx_size, pd->plane_type, block);
   const int eob = decode_coefs(xd, pd->plane_type,
-                               BLOCK_OFFSET(pd->dqcoeff, block), tx_size,
+                               pd->dqcoeff, tx_size,
                                dequant, ctx, so->scan, so->neighbors, r);
   vp9_set_contexts(xd, pd, plane_bsize, tx_size, eob > 0, x, y);
   return eob;