Allocate dual buffer sets for encoding

Allocate dual buffer sets for encoding

Allocate memory space of dual buffer sets that store the coeff, qcoeff,
dqcoeff, and eobs. Connect the pointers of macroblock_plane and
macroblockd_plane to the actual buffer in use accordingly.

Change-Id: I2f0b5f482ca879fae39095013eaf8901db20a5a4