Immigrate tokenize_mb into tokenize_sb

Unify the tokenize_ function and enable configurable block size for
superblock 8x8. We are immigrating the functionalities of
macroblock handles into superblock ones, and eventually will remove
encode_mb and decode_mb. To be continued on detokenize_ module.

Change-Id: I9f81e8c2291082535cf5e0c4b662eb24fb7c8a7f