Multisymbol BR coding is simplified as follows.
1. Remove computation of level counts by using a template of size 8;
2. Context is derived by using a template of size 3.
3. lps and eob probabilities are trained.
4. Share contexts between TX_16X16 and above.

The number of probability values used in BR coding are reduced from 1152 to 378.

Change-Id: I0419127e871f9e566c2489aa4b1825c5364aec5a