Add MSA optimized ARGBToRGB565Row_MSA, ARGBToARGB1555Row_MSA, ARGBToARGB4444Row_MSA, ARGBToUV444Row_MSA functions

R=fbarchard@google.com
BUG=libyuv:634

Performance Gain (vs C vectorized)
ARGBToRGB565Row_MSA       - ~1.6x
ARGBToRGB565Row_Any_MSA   - ~1.6x
ARGBToARGB1555Row_MSA     - ~1.3x
ARGBToARGB1555Row_Any_MSA - ~1.3x
ARGBToARGB4444Row_MSA     - ~3.8x
ARGBToARGB4444Row_Any_MSA - ~3.8x
ARGBToUV444Row_MSA        - ~2.4x
ARGBToUV444Row_Any_MSA    - ~2.4x

Performance Gain (vs C non-vectorized)
ARGBToRGB565Row_MSA       - ~2.8x
ARGBToRGB565Row_Any_MSA   - ~2.8x
ARGBToARGB1555Row_MSA     - ~2.2x
ARGBToARGB1555Row_Any_MSA - ~2.2x
ARGBToARGB4444Row_MSA     - ~6.8x
ARGBToARGB4444Row_Any_MSA - ~6.6x
ARGBToUV444Row_MSA        - ~6.7x
ARGBToUV444Row_Any_MSA    - ~6.7x

Review URL: https://codereview.chromium.org/2520003004 .