Update filters to use skvx instead of SkNx

Change-Id: I1a5490f546a3cb046c64b114a30be991d2d9f2cc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/541064
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
5 files changed