A new experiment for deblocking filter that separates vertical
and horizontal filter strengths. This experiment is based on the
assumption that non-flatness characteristics of vertical and
horizontal direction may differ. Therefore selecting different
filter strengths for vertical and horizontal can improve deblocking
performance.

The process of finding proper filter strength:
1. Search through the filter level under the constraint that
   (vertical == horizontal), and find the best solution.
2. Fix vertical level as the best solution found in step 1 and vary
   horizontal level to find the best value.
3. Fix the selected horizontal level, vary vertical level to find
   its best value.

The experiment is working with UV_LVL, sharing the same config flag.
The searching for horizontal and vertical filter strength only applies
on Y plane for now.

The experimental flag should be changed to filter_level later.

Change-Id: I164eec8d3ccb3da7ff109c5c55f4b52c1536ddf1