add vroundps, impl Op::floor on x86

Change-Id: Iad94adda2da74fefb5657d883120f85ad362327e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/263461
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed