H010 is 10 bit planar format with 10 bits in lower bits.
P010 is 10 bit biplanar format with 10 bits in upper bits.
This function weaves the U and V channels and shifts the bits
into the upper bits.

Bug: libyuv:751
Test: LibYUVPlanarTest.MergeUV10Row_Opt
Change-Id: I4a0bac0ef1ff95aa1b8d68261ec8e8e86f2d1fbf
Reviewed-on: https://chromium-review.googlesource.com/752692Reviewed-by: Cheng Wang <wangcheng@google.com>
Reviewed-by: Frank Barchard <fbarchard@google.com>
Commit-Queue: Frank Barchard <fbarchard@google.com>