Moving txfm_size bits before prediction mode bits.

Moving txfm_size bits before prediction mode bits.

Hardware implementation needs to load coeff probs based on the
transform size. For selectable transform size, moving these bits
earlier in the bitstream adds some delay giving time to preload
the probs and speeds up the decoding process.

Change-Id: I3bfc1f662ae6f219c9286fe9ae6310c7d8a63ea7