Revert of Code's more readable when SkPMFloat is an Sk4f. (patchset #3 id:40001 of https://codereview.chromium.org/1061603002/)

Reason for revert:
missed some neon code

Original issue's description:
> Code's more readable when SkPMFloat is an Sk4f.
>  #floats
>
> BUG=skia:
> BUG=skia:3592
>
> Committed: https://skia.googlesource.com/skia/+/6b5dab889579f1cc9e1b5278f4ecdc4c63fe78c9

TBR=reed@google.com,mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1056143004
8 files changed