vp9: Non-rd pickmode: fix to add ARF mode entries to THR_MODES.
vp9: Non-rd pickmode: fix to add ARF mode entries to THR_MODES.

BUG=webm:1359

Change-Id: Ie0c66efa2e19d1ec9c744d14e3fa8f1e6214cdd6

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