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

Performance Gain (vs C vectorized)
TransposeWx16_MSA        - ~6.0x
TransposeWx16_Any_MSA    - ~4.7x
TransposeUVWx16_MSA      - ~6.3x
TransposeUVWx16_Any_MSA  - ~5.4x

Performance Gain (vs C non-vectorized)
TransposeWx16_MSA        - ~6.0x
TransposeWx16_Any_MSA    - ~4.8x
TransposeUVWx16_MSA      - ~6.3x
TransposeUVWx16_Any_MSA  - ~5.4x

Review-Url: https://codereview.chromium.org/2617703002 .