vp9: Sample encoder vpx_temporal_svc_encoder: enable row-mt
vp9: Sample encoder vpx_temporal_svc_encoder: enable row-mt

Enable row-mt in the sample encoder vpx_temporal_svc_encoder.c,
under certain condiitons.

Change-Id: Ic103ee81a9d80be5bf6e5778cc21fc3199db909d

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