move sk_memset16,32,64 out-of-line

move sk_memset16,32,64 out-of-line

This helps pick it out on profiles and when debugging.

This will have a negligible impact on speed in most cases (small memsets are always fast, large memsets dwarf function call overhead), and clients like Chrome that use link-time optimization should see exactly zero impact.

This does however affect code size: it makes libskia 43K smaller on my laptop.

Change-Id: I55bdc75b7429a63024ab3b7d55dc1f886bde102a
Reviewed-on: https://skia-review.googlesource.com/6589
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>