BUG=libyuv:634

Change-Id: If8d60bd57f01fe95bc2fd26196466574195cc126

Performance Gain (vs C auto-vectorized)
InterpolateRow_MSA      - ~3.3x
InterpolateRow_Any_MSA  - ~2.5x
ARGBSetRow_MSA          - ~1.0x
ARGBSetRow_Any_MSA      - ~1.0x
ARGBToRGB24Row_MSA      - ~1.9x
ARGBToRGB24Row_Any_MSA  - ~1.6x
MergeUVRow_MSA          - ~1.6x
MergeUVRow_Any_MSA      - ~1.2x

Performance Gain (vs C non-vectorized)
InterpolateRow_MSA      - ~11.3x
InterpolateRow_Any_MSA  - ~ 7.9x
ARGBSetRow_MSA          - ~ 6.2x
ARGBSetRow_Any_MSA      - ~ 4.0x
ARGBToRGB24Row_MSA      - ~ 9.9x
ARGBToRGB24Row_Any_MSA  - ~ 8.4x
MergeUVRow_MSA          - ~12.7x
MergeUVRow_Any_MSA      - ~ 8.0x

Change-Id: If8d60bd57f01fe95bc2fd26196466574195cc126
Reviewed-on: https://chromium-review.googlesource.com/445817Reviewed-by: Frank Barchard <fbarchard@google.com>
Commit-Queue: Frank Barchard <fbarchard@google.com>