Instead of using the predict buffer, the decoder now writes
the predictor into the recon buffer.  For blocks with eob=0,
unnecessary idcts can be eliminated.  This gave a performance
boost of ~1.8% for the HD clips used.

Tero: Added needed changes to ARM side and scheduled some
      assembly code to prevent interlocks.

Patch Set 6:  Merged (I1bcdca7a95aacc3a181b9faa6b10e3a71ee24df3)
into this commit because of similarities in the idct
functions.
Patch Set 7: EC bug fix.

Change-Id: Ie31d90b5d3522e1108163f2ac491e455e3f955e6