drm/i915/selftests: Add a cancel request selftest that triggers a reset

Add a cancel request selftest that results in an engine reset to cancel
the request as it is non-preemptable. Also insert a NOP request after
the cancelled request and confirm that it completes successfully.

v2:
 (Tvrtko)
  - Skip test if preemption timeout compiled out
  - Skip test if engine reset isn't supported
  - Update debug prints to be more descriptive
v3:
  - Add comment explaining test
v4:
 (John Harrison)
  - Fix typos in comment explaining test
  - goto out_rq is NOP creation fails

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220113181351.21296-2-matthew.brost@intel.com