use fma in store_8888

I think we just happened not to here.  This improves Adobe -> sRGB pipeline conversion by about 3-4%.

While at it, unify all the fma() lambdas into SkNf_fma().  I'd have called it fma(), but IIRC there was some sort of name conflict there with type-generic fma() functions from the C math.h or something silly like that.

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

Change-Id: Id176671fec27c984efa4703c5be2fb63b7f0b11f
Reviewed-on: https://skia-review.googlesource.com/5474
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed