I422ToUYVYRow_AVX2 optimized from 7 cycles per 32 pixels to 4.6 cycles.
Instead of 2 vpermq and vpunpcklbw:
vmovdqu    (%1),%%xmm2
vmovdqu    0x00(%1,%2,1),%%xmm3
vpermq     $0xd8,%%ymm2,%%ymm2
vpermq     $0xd8,%%ymm3,%%ymm3
vpunpcklbw %%ymm3,%%ymm2,%%ymm2

..use vpmovzxbd to expand the bytes to shorts, then vpslld and vpor
vpmovzxbd  (%1),%%ymm2
vpmovzxbd  0x00(%1,%2,1),%%ymm3
vpslld     $0x10,%%ymm3,%%ymm3
vpor       %%ymm3,%%ymm2,%%ymm2
which reduces the port 5 bottleneck by 1 cycle.

Bug: libyuv:556
Test: out/Release/libyuv_unittest --gtest_filter=*I42?To*UY*Opt

Change-Id: I53799e53cc6b090a1a695c839094c193be3eecaf
Reviewed-on: https://chromium-review.googlesource.com/899873
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: richard winterton <rrwinterton@gmail.com>
Reviewed-by: Cheng Wang <wangcheng@google.com>