Single pass upsample with bilinear filter.
NEON version optimized - Pixel Sailfish QC821

Was TestScaleRowUp2_16 (5741 ms)
Now TestScaleRowUp2_16 (4484 ms)
C   TestScaleRowUp2_16 (6555 ms)

TBR=kjellander@chromium.org
BUG=libyuv:718
TEST=LibYUVScaleTest.TestScaleRowUp2_16 (709 ms)

Change-Id: Ib04ceb53e0ab644a392c39c3396e313530161d92
Reviewed-on: https://chromium-review.googlesource.com/646701Reviewed-by: Frank Barchard <fbarchard@google.com>
Reviewed-by: Cheng Wang <wangcheng@google.com>