I420 and I422 To YUY2 and UYVY ported from SSE2 to AVX2.

Was SSE2
I420ToYUY2_Opt (135 ms)
I420ToUYVY_Opt (148 ms)
I422ToYUY2_Opt (145 ms)
I422ToUYVY_Opt (142 ms)

Now AVX2
I420ToYUY2_Opt (133 ms)
I420ToUYVY_Opt (130 ms)
I422ToYUY2_Opt (127 ms)
I422ToUYVY_Opt (137 ms)

Bug: libyuv:556
Test: out/Release/libyuv_unittest --sandbox_unittests --gtest_filter=*I42?To*UY*Opt
Change-Id: Ic35f97cee02dc009fd98785589ba17c7cf50bb35
Reviewed-on: https://chromium-review.googlesource.com/892493
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: richard winterton <rrwinterton@gmail.com>