SkOpts_hsw ODR paranoia

I'm warming back up to the idea of very careful use of SkOpts_hsw.
But if we're going to do that, we need a strict header discipline.
No header can be assumed to be safe without vetting, and most aren't.

Today there's only one function defined in SkOpts_hsw, so this CL mostly
rewrites that convolve_vertically() to use no headers beyond immintrin.h
and stdint.h, both safe.  It shared very little code with the others
anyway, so we're not losing anything by putting it directly into
SkOpts_hsw.cpp.  I have also streamlined the implementation considerably
to improve maintainability and readability.

Change-Id: Ia03daae660e54125a0d2e2988464cfc930349e80
Reviewed-on: https://skia-review.googlesource.com/7611
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed