Further improve macroblock loop filters

Further improve macroblock loop filters

This change included:
1. Aligned reads in vp9_mbloop_filter_vertical_edge function.
Since we actually read 16 bytes, we can align the reads to read
starting at (s - 8) instead of (s - 5).
2. Combined u, v loop filters.
3. Added 8x16 transpose.

This gave 2% decoder performance gain (tulip clip).

Change-Id: Ib14c2f1645c4a3436df17fe2f24789506bf0bb58