Doing tokenize in the last step of RD loop and then doing packing
tokens in bitstream packing phase is hard for debugging.

Therefore, we create a frame-level buffer to store the txfm coeffs
from the reconstruction in RD loop and then in bitstream packing
phase, we can code the txfm coeffs directly.

Change-Id: I999470eef6e038317a91585df2bdfc20aca3573e