[kernel][arch] Apply style changes

Previous change had outstanding comments (after change was merged),
this CL addresses those comments.

* Use 2 space indentation on new ASM files.
* Unconditionally add arch/$zircon_cpu/user-copy:tests to kernel tests.

No functional changes.

Test: fx build
Change-Id: I9d4612f8e5caee93ee9a71250b3197302b37bfe3
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/695921
Reviewed-by: Roland McGrath <mcgrathr@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
Fuchsia-Auto-Submit: Gianfranco Valentino <gevalentino@google.com>