Bug 1061339 - Enable AVX2 in libvpx for VS2012+. r=giles

--HG--
rename : media/libvpx/vp8_rtcd_x86-win32-vs8.h => media/libvpx/vp8_rtcd_x86-win32-vs11.h
rename : media/libvpx/vp8_rtcd_x86_64-win64-vs8.h => media/libvpx/vp8_rtcd_x86_64-win64-vs11.h
rename : media/libvpx/vp9_rtcd_x86-win32-vs8.h => media/libvpx/vp9_rtcd_x86-win32-vs11.h
rename : media/libvpx/vp9_rtcd_x86_64-win64-vs8.h => media/libvpx/vp9_rtcd_x86_64-win64-vs11.h
rename : media/libvpx/vpx_config_x86-win32-vs8.asm => media/libvpx/vpx_config_x86-win32-vs11.asm
rename : media/libvpx/vpx_config_x86-win32-vs8.h => media/libvpx/vpx_config_x86-win32-vs11.h
rename : media/libvpx/vpx_config_x86_64-win64-vs8.asm => media/libvpx/vpx_config_x86_64-win64-vs11.asm
rename : media/libvpx/vpx_config_x86_64-win64-vs8.h => media/libvpx/vpx_config_x86_64-win64-vs11.h
rename : media/libvpx/vpx_scale_rtcd_x86-win32-vs8.h => media/libvpx/vpx_scale_rtcd_x86-win32-vs11.h
rename : media/libvpx/vpx_scale_rtcd_x86_64-win64-vs8.h => media/libvpx/vpx_scale_rtcd_x86_64-win64-vs11.h