intrapred/d135: flatten border results before storing
intrapred/d135: flatten border results before storing

the results along the top and left border are then stored with a moving
window into the vector.
~40-67% faster on ARM, ~40-77+% on x86 depending on the block size.

Change-Id: Iab369aa2946a3ae4eb7290d512868fe5db92dbc8

mbebenita/aom,mbebenita/aom,mwgoldsmith/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,Topopiccione/libvpx,ShiftMediaProject/libvpx,mbebenita/aom,Topopiccione/libvpx,ittiamvpx/libvpx-1,webmproject/libvpx,ShiftMediaProject/libvpx,luctrudeau/aom,luctrudeau/aom,smarter/aom,mwgoldsmith/libvpx,smarter/aom,mwgoldsmith/vpx,mwgoldsmith/libvpx,webmproject/libvpx,luctrudeau/aom,ShiftMediaProject/libvpx,mbebenita/aom,ShiftMediaProject/libvpx,GrokImageCompression/aom,mbebenita/aom,smarter/aom,smarter/aom,GrokImageCompression/aom,webmproject/libvpx,mwgoldsmith/libvpx,ittiamvpx/libvpx-1,Topopiccione/libvpx,mbebenita/aom,webmproject/libvpx,GrokImageCompression/aom,mbebenita/aom,ittiamvpx/libvpx-1,mbebenita/aom,smarter/aom,smarter/aom,ittiamvpx/libvpx-1,Topopiccione/libvpx,ittiamvpx/libvpx-1,mwgoldsmith/vpx,mwgoldsmith/libvpx,Topopiccione/libvpx,mbebenita/aom,mwgoldsmith/vpx,webmproject/libvpx,luctrudeau/aom,GrokImageCompression/aom,GrokImageCompression/aom,luctrudeau/aom,mwgoldsmith/vpx,mwgoldsmith/vpx,mwgoldsmith/vpx,ittiamvpx/libvpx-1,luctrudeau/aom,GrokImageCompression/aom,Topopiccione/libvpx,ShiftMediaProject/libvpx