Implement log2_fast for vp9_nb_mvs_inconsistency
Implement log2_fast for vp9_nb_mvs_inconsistency

This speed up non_greedy_mv by 8.7%

Change-Id: Ia46e3e7c4d32ec364091fad26cc953c62963e526

webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx