Rework coeff probability model update for rtc coding

Rework coeff probability model update for rtc coding

This commit reworks the ONE_LOOP_REDUCED coefficient probability
model update process. It allows model update for every coefficient
across the spectrum at a coarser resolution, instead of performing
precise update only for certain subset of probability models.

The overall runtime remains nearly same (<1% change) for speed -6.
The compression performance is improved by 7.5% in PSNR for speed
-5 and 4.57% for speed -6, respectively.

Change-Id: Ifb17136382ee7e39a9f34ff4a4f09a753125c8d1