The debugfs files 'dev_state' and 'dev_timeout' are added.
Users can query the current queue stop status through these two
files. And set the waiting timeout when the queue is released.

dev_state: if dev_timeout is set, dev_state indicates the status
of stopping the queue. 0 indicates that the queue is stopped
successfully. Other values indicate that the queue stops fail.
If dev_timeout is not set, the value of dev_state is 0;

dev_timeout: if the queue fails to stop, the queue is released
after waiting dev_timeout * 20ms.
Signed-off-by: Weili Qian <qianweili@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>