Optimized C-code of the following functions:
 - vp8_tokenize_mb
 - tokenize1st_order_b
 - tokenize2nd_order_b
Gives ~1-5% speed-up for RT encoding on Cortex-A8/A9
depending on encoding parameters.

Change-Id: I6be86104a589a06dcbc9ed3318e8bf264ef4176c