Reduce call num of exhaustive search

The encoding time difference between non_greedy_mv and baseline
is reduced from 51% to 13%

However, there is also a performance impact.

non_greedy_mv performance:
Before this CL
lowres 0.395% midres 0.716% hdres 0.533%
After this CL
lowres 0.242% midres 0.429% hdres 0.305%

Change-Id: I047d6509df504b264981c0b903c0cc955f45b273
4 files changed