Move sk_memset* from SkUtils to SkOpts

This is a (hopefully) more careful reland of parts of
https://skia-review.googlesource.com/c/skia/+/464876

Change-Id: I32dd6777a70d983d8a66a4bf9557cab6e3d7ebc2
Bug: skia:12584
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/467124
Reviewed-by: Greg Daniel <egdaniel@google.com>
22 files changed