Optimize partition search order

This commit change the partition search order to allow checking of
rectangular partition to be done after square partitions. It also
added a speed feature to skip rectangular partition check when
NONE is better than SPLIT in RD sense.

This feature roughly speed up encoder by 1.5X with loss on compression
-0.91% on cif set
-0.56% on stdhd set

Change-Id: I0d2d06993041aa9ea9073fcc39c54f73a127dfa4