In SPLITMV, the 8x8 segment will be checked first.  If the 8x8 rd
is better than the best, we check the other segments.  Otherwise
bail.  Adjustments to the thresh_mult were necessary to make
up for the initial quality loss.
The performance improved by 20% (average) for good quality,
speed 0 and speed 1, while the overall quality remained the same.

Change-Id: I717aef401323c8a254fba3e9777d2a316c774cc3