tests/perf_pmu: Verify busyness when PMU is enabled after engine got busy

Make sure busyness is correctly reported when PMU is enabled after the
engine is already busy with a single long batch.

v2:
 * Make the sleep unconditional and use scientific notiation for large
   constants. (Chris Wilson)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
1 file changed