[Intel-gfx] i-g-t dummyload/spin batch v8

[Abdiel Janulgue]

Changes:

* lib/dummyload: Add a helper to terminate recursive batch
  manually.
* gem_wait: Restore sanitycheck wait on the recursive batch and
  avoid using C99 locals.
* kms_flip: Don't wait on the fb - should be busy. Exit the
  spin batch when flip is queued
* kms_busy: Tidy up finish_fb_busy

- Abdiel