The tx_type becomes dummy when lv_map is on. The tx_type search
will be performed in av1_search_txk_type() and the results will be
stored in txk_type[]

In choose_tx_size_type_from_rd, we use best_txk_type[] to record
the best search result within different tx_size.

Change-Id: I67c489d261aecaa0092e0cc562670588c6c55941