Switch YUV conversion macro to output 16 bits per channel.
STOREAR30 macro to output AR30.

[ RUN      ] LibYUVConvertTest.TestH420ToARGB
uniques: B 220, G, 220, R 220
[       OK ] LibYUVConvertTest.TestH420ToARGB (0 ms)
[ RUN      ] LibYUVConvertTest.TestH010ToARGB
uniques: B 256, G, 256, R 256
[       OK ] LibYUVConvertTest.TestH010ToARGB (0 ms)
[ RUN      ] LibYUVConvertTest.TestH010ToAR30
uniques: B 883, G, 883, R 883
[       OK ] LibYUVConvertTest.TestH010ToAR30 (0 ms)

Bug: libyuv:751
Test: LibYUVConvertTest.H010ToAR30_Opt
Change-Id: I902b718e2c8b68ede69625ccafebc6519d5af70d
Reviewed-on: https://chromium-review.googlesource.com/869511Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: richard winterton <rrwinterton@gmail.com>
Commit-Queue: Frank Barchard <fbarchard@chromium.org>