Enable various thresholds of motion detection

Enable various thresholds of motion detection

This commit changed to enable the encoder to adjust motion dection
speed threshold based on picture size. In addition, cpu-used 1 now
does a partition search every other frame instead of every third
frame for low resolution inputs.

The change has no quality/speed impact for 720p and above. Test
showed the change increase encoding time by between 3% to 6% for
cpu-used 2 encodiong of 360p sequences. It also has a compression
gain about .3%.

For cpu-used 2, the change resolved some very disturbing visual
artifacts in certain sequences when large block partitionings and
transforms are used as a result of copying the partition from a
previous frame.

Change-Id: Ic7fd22508cdb811d4ca935655adbf20109286cfa