finish up load4/store4 refactoring

I saved the easiest for last.  No generated code diff for store_f32.
This just moves the platform-specific code over to SkJumper_vectors.h

Also clarify types in the existing load4()/store4() functions.

SkJumper_stages.cpp looks good to start growing again!

Change-Id: I6a8599d090b4e17663703b0c0325dbe550a6cdd8
Reviewed-on: https://skia-review.googlesource.com/11348
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed