The br_cdf and lps_cdf with a new 4-state symbol br_cdf.
The br symbol indicates whether the level is k, k+1, k+2 or >k+2
In the latter case, a new br symbol is read. Up to 4 br symbols are
read which will reach level 14 at most. Levels greater than 14 are
golomb coded.

The adapted symbol count is reduced further by this commit.
E.g. for the I-frame of ducks_take_off at cq=12, the number of adapted symbols
is reduced from 4.27M to 3.85M. About 10% reduction.

Gains seems about neutral on a limitied subset.

Change-Id: I294234dbd63fb0fa26aef297a371cba80bd67383