Turn off global motion for sub8x8 blocks

Lowres: 0.03% improvement, 1% improvement on waterfall_cif.y4m
Midres: 0.085% overall improvement, 1.253% improvement on station2_480p25.y4m
Change-Id: I3872934d978bb4ca828c6b9acd2fdb951d9da299
6 files changed