A more complicated store variant to stress inter-engine dependencies
(i.e. semaphores and sync). We write a control value from one batch into
the next and then execute it. This is repeated a few times with each
execution happening on a different engine (so the kernel has to
serialise operations between engines) until we finally write the value
out into our scratch buffer where we can check the result, just like a
Chinese whisper.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
