WIP: removing predictor buffer usage from decoder

This patch will use the dest buffer instead of the
predictor buffer.  This will allow us in future commits
to remove the extra mem copy that occurs in the dequant
functions when eob == 0.  We should also be able to remove
extra params that are passed into the dequant functions.

Change-Id: I7241bc1ab797a430418b1f3a95b5476db7455f6a