port S32_alpha_D32_filter_DX to SkOpts

I'll follow up by moving all the other things that live
in src/opts today into SkBitmapProcState.cpp... they
only use SSE2 or NEON, and don't need runtime detection.

There's lots of refactoring to do here still, and I've
mostly resisted the urge until this code is all in one place.

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Idea34a03c46d79b0fd6fbef1a49aaf27961c8260
Reviewed-on: https://skia-review.googlesource.com/c/171582
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
17 files changed