Now that we can atomically acquire the engine wakeref, make use of it
when check whether the RING registers are idle.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190812091045.29587-7-chris@chris-wilson.co.uk