x86/lossless_videodsp: silly one-line cosmetic.
x86/vp9lpf: faster P7..Q7 accesses.

Introduce 2 additional registers for stride3 and mstride3 to allow
direct accesses (and lea drops).

Also uses defines to clarify the code.
x86/vp9lpf: refactor v/h using common macros for P7 to Q7.
x86/vp9lpf: add ff_vp9_loop_filter_[vh]_88_16_{ssse3,avx}.

9680 decicycles in loop_filter_v_88_16_c, 4193765 runs, 539 skips
9233 decicycles in loop_filter_h_88_16_c, 4193751 runs, 553 skips

1932 decicycles in ff_vp9_loop_filter_v_88_16_ssse3, 4194162 runs, 142 skips
3058 decicycles in ff_vp9_loop_filter_h_88_16_ssse3, 4193877 runs, 427 skips

Adding SSE2 support should be relatively trivial (just a matter of
changing the pshufb with [mask_mix]), patch welcome.