This commit makes the inter prediction buffer system to support
hybrid partition search. It reduces the runtime of speed -5 by
about 3%. No compression performance change.

vidyo1 720p 1000 kbps
11831 ms -> 11497 ms

nik 720p 1000 kbps
10919 ms -> 10645 ms

Change-Id: I5b2da747c6395c253cd074d3907f5402e1840c36