libvpx

Run sub-pixel motion search for NEWMV mode test

As Yunqing suggested, this commit makes non-RD mode decision always run
sub-pixel motion search in NEWMV mode. The compression performance
gains becomes fairly significant after we enabled sub-pixel accuracy
motion compensated prediction to calculate SAD cost.

For test sequences pedestrian_area at 1080p and vidyo1 at 720p, the
runtime goes slower by 5%. For rtc test set, the compression performance
is improved by 21.20%.

Change-Id: I38cbfdd5c53d79423e1fafb3154f8ddeed63bbf0