vp8/x86: move variable assigned inside macro branch.

The value is not used outside the branch.
vp9/x86: store unpacked intermediates for filter6/14 on stack.

filter16 goes from 508 to 482 (h) or 346 to 314 (v) cycles; filter88
goes from 240 to 238 (h) or 174 to 165 (v) cycles, measured on TOS.
vp8/x86: save one register in SIGN_ADD/SUB.
vp9/x86: make filter_44_v work on 32-bit.
vp9/x86: make filter_88_v work on 32-bit.
vp9/x86: make filter_48/84_v work on 32-bit.
vp9/x86: make filter_16_v work on 32-bit.
vp9/x86: make filter_44_h work on 32-bit.
vp9/x86: make filter_48/84/88_h work on 32-bit.
vp9/x86: make filter_16_h work on 32-bit.
vp9/x86: add myself to copyright holders for loopfilter assembly.