implement a whole slew of arm64 ops

This adds assembler support for a bunch of ARM instructions and uses
them to implement a bunch of SkVM ops.  No diffs.

movs() seems strictly more useful than fmovs(), so I've replaced it.

Change-Id: Ied38a44461653598269421b0b56bef4eb19bb1e9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/335918
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed