VFs call adf_dev_stop() from a PF to VF interrupt bottom half.
This causes an oops "scheduling while atomic", because it tries
to acquire a mutex to un-register crypto algorithms.
This patch fixes the issue by calling adf_dev_stop() asynchronously.

Changes in v2:
 - change kthread to a work queue.
Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>