kms_atomic_transition subtest modeset-transition-nonblocking is flaky

In our CI, this test fails occasionally across multiple platforms. The failure happens in the commit_display function where igt_display_commit_atomic asserts due to igt_display_try_commit_atomic returning -EBUSY.

If I modify the test to retry when the commit returns -EBUSY, as is done in other tests which work with nonblocking commits, the test passes consistently.

I'm happy to send a change to address this, but would like some guidance as to the preferred way to fix this. I can see a few options:

1. In commit_display replace the call to igt_display_commit_atomic with a retry loop
2. In igt_display_commit_atomic add retry logic to handle -EBUSY
3. Add a new function igt_display_commit_atomic_retry to igt_kms.c which does the return logic (and leave igt_display_commit_atomic untouched) and call this new function from commit_display