Merge commit '715f139c'

* commit '715f139c': (23 commits)
  vp9lpf/x86: make filter_16_h work on 32-bit.
  vp9lpf/x86: make filter_48/84/88_h work on 32-bit.
  vp9lpf/x86: make filter_44_h work on 32-bit.
  vp9lpf/x86: make filter_16_v work on 32-bit.
  vp9lpf/x86: make filter_48/84_v work on 32-bit.
  vp9lpf/x86: make filter_88_v work on 32-bit.
  vp9lpf/x86: make filter_44_v work on 32-bit.
  vp9lpf/x86: save one register in SIGN_ADD/SUB.
  vp9lpf/x86: store unpacked intermediates for filter6/14 on stack.
  vp9lpf/x86: move variable assigned inside macro branch.
  vp9lpf/x86: simplify ABSSUM_CMP by inverting the comparison meaning.
  vp9lpf/x86: remove unused register from ABSSUB_CMP macro.
  vp9lpf/x86: slightly simplify 44/48/84/88 h stores.
  vp9lpf/x86: make cglobal statement more conservative in register allocation.
  vp9lpf/x86: save one register in loopfilter surface coverage.
  vp9lpf/x86: add ff_vp9_loop_filter_[vh]_44_16_{sse2,ssse3,avx}.
  vp9lpf/x86: add ff_vp9_loop_filter_h_{48,84}_16_{sse2,ssse3,avx}().
  vp9lpf/x86: add an SSE2 version of vp9_loop_filter_[vh]_88_16
  vp9lpf/x86: add ff_vp9_loop_filter_[vh]_88_16_{ssse3,avx}.
  vp9lpf/x86: add ff_vp9_loop_filter_[vh]_16_16_sse2().
  ...

All these commits are cherry-picks from FFmpeg. Maybe some slight
differences sneaked in but the Libav codebase still differs too much
with our own to make a proper diff. This merge is a noop.
Merged-by: Clément Bœsch <u@pkh.me>