vp9: Disable usage of sb_use_mv_part for SVC.
vp9: Disable usage of sb_use_mv_part for SVC.

To fix valgrind issueis with SVC tests.
SVC encoding uses prune_evenmore which is causing uinit value.

Will re-enable later when issue is resolved.

Change-Id: I257ff878cf78197ddd813db056582a4d5fe94f44

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