Allocate four |zcoeff_blk| for sub8x8 contexts.
Allocate four |zcoeff_blk| for sub8x8 contexts.

The RD and load save/code grabs it as groups of four. In practice there
is no change to physical allocations becaquse this is backed by a 16-byte
memalign.

Change-Id: I01e89769872300e23227e03dd24a6e229f482025

VTCSecureLLC/libvpx,webmproject/libvpx,running770/libvpx,mbebenita/aom,thdav/aom,VTCSecureLLC/libvpx,mwgoldsmith/vpx,felipebetancur/libvpx,thdav/aom,smarter/aom,Topopiccione/libvpx,ittiamvpx/libvpx-1,shacklettbp/aom,mwgoldsmith/vpx,Topopiccione/libvpx,shyamalschandra/libvpx,luctrudeau/aom,GrokImageCompression/aom,openpeer/libvpx_new,ShiftMediaProject/libvpx,Topopiccione/libvpx,openpeer/libvpx_new,running770/libvpx,zofuthan/libvpx,shacklettbp/aom,VTCSecureLLC/libvpx,liqianggao/libvpx,thdav/aom,mwgoldsmith/vpx,webmproject/libvpx,shyamalschandra/libvpx,shyamalschandra/libvpx,ShiftMediaProject/libvpx,luctrudeau/aom,thdav/aom,smarter/aom,VTCSecureLLC/libvpx,webmproject/libvpx,liqianggao/libvpx,shacklettbp/aom,ittiamvpx/libvpx-1,luctrudeau/aom,smarter/aom,openpeer/libvpx_new,zofuthan/libvpx,luctrudeau/aom,jmvalin/aom,shyamalschandra/libvpx,mbebenita/aom,jmvalin/aom,felipebetancur/libvpx,mwgoldsmith/vpx,openpeer/libvpx_new,jmvalin/aom,liqianggao/libvpx,mwgoldsmith/libvpx,thdav/aom,felipebetancur/libvpx,liqianggao/libvpx,ittiamvpx/libvpx-1,zofuthan/libvpx,mbebenita/aom,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,thdav/aom,openpeer/libvpx_new,GrokImageCompression/aom,felipebetancur/libvpx,luctrudeau/aom,running770/libvpx,GrokImageCompression/aom,liqianggao/libvpx,ittiamvpx/libvpx-1,zofuthan/libvpx,Topopiccione/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,felipebetancur/libvpx,mbebenita/aom,mbebenita/aom,shyamalschandra/libvpx,Topopiccione/libvpx,shacklettbp/aom,running770/libvpx,jmvalin/aom,smarter/aom,GrokImageCompression/aom,shyamalschandra/libvpx,luctrudeau/aom,Topopiccione/libvpx,VTCSecureLLC/libvpx,felipebetancur/libvpx,jmvalin/aom,running770/libvpx,openpeer/libvpx_new,mwgoldsmith/vpx,mbebenita/aom,mbebenita/aom,liqianggao/libvpx,webmproject/libvpx,zofuthan/libvpx,GrokImageCompression/aom,VTCSecureLLC/libvpx,smarter/aom,webmproject/libvpx,jmvalin/aom,running770/libvpx,ittiamvpx/libvpx-1,shacklettbp/aom,mwgoldsmith/libvpx,zofuthan/libvpx,smarter/aom,GrokImageCompression/aom,mwgoldsmith/libvpx,shacklettbp/aom,webmproject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,ittiamvpx/libvpx-1,mbebenita/aom,mbebenita/aom,mwgoldsmith/libvpx