Use rate/distortion thresholds to control non-RD partition search

Use rate/distortion thresholds to control non-RD partition search

Compare the estimated rate and distortion to the thresholds scaled
according to the operating block size and determine if further
split partition search will be run. The compression performance of
speed -5 is changed by -0.074%. The encoding speed is 10% - 15%
faster.

vidyo1 720p
16545 b/f, 40.492 dB, 11475 ms -> 16535 b/f, 40.486 dB, 10100 ms

nik720p
16624 b/f, 36.310 dB, 10071 ms -> 16617 b/f, 36.313 dB, 8346 ms

Change-Id: Ic9197ab5761279ae55d2fb7813b2af0e0db497b8