When experiment LOOPFILTER_LEVEL is on, there're four base filter levels
for each frame. This patch enables one to use one delta or four deltas
to update corresponding filter levels for each superblock in
EXT_DELTA_Q.

1 bit per frame is sent through bitstream to select one or four deltas.
Now, we hard code to use one delta.

Change-Id: I9c61a035064fa81878b0575ad21664e2b22a6a45