rename skvm norm() to mag(), move it where used

It's a lot simpler inline than in SkVM.h.

Change-Id: I46fd27ede14dee5dc23d2a13d6c189847e816145
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/341799
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
2 files changed