Add try_self_level_down() and get_level_prob()

try_self_level_down() computes the cost difference of the coeff
that is downgraded by one level

get_level_prob() computes the probability of level_map coding
at a specific position and level.

Change-Id: Iaa9d40477aaf798993c2d5d26341551db665902b
1 file changed