While sorting, preserving the order of the rest of the list when moving
an element to the top of list makes hardware implementation much simpler.

The compression performance is roughly same: overall, avg performance on
screen-content set is 0.137% better than before in fact.

Bug=aom:127

Change-Id: Id1aa1e90254b44eae9133b47bca8f853f6a62c6b