Search for tx size using only DCT and 1D DCT first; then do an
additional round of tx type search with tx sizes already decided.

If enabled on speed 1, quality drop is 0.2% on lowres and midres;
average encoding speed up 20% (15~30% depending on sequences).

Currently enabled for speed >= 2.

Change-Id: I62526a501ab4db54c91d2bc506dadf9fc141bd03