split up SkColor_opts_SSE2.h

Lots of dead code deleted, and the rest moved where it's used.

Change-Id: I78804ce8563685b0b6aea7e8eb8a6656771d73fe
Reviewed-on: https://skia-review.googlesource.com/c/174286
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed