Rework set_offsets() for rd search
Rework set_offsets() for rd search

Factor out the segment_id setup from mi array alignment.

Change-Id: I345ad7ea7b6c9edb6f86224e1941f2c954d68ff3

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