This switches over SkXfermodes_opts.h and SkColorMatrixFilter to use Sk4f,
and converts the SkPMFloat benches to Sk4f benches.
No pixels should change here, and no code beyond the Sk4f_ benches should change speed.
The benches are faster than the old versions.
BUG=skia:4117
Review URL: https://codereview.chromium.org/1324743002
