Before this stateless decoder driver can leave the staging area:
* The Request API needs to be stabilized;
* The codec-specific controls need to be thoroughly reviewed to ensure they
  cover all intended uses cases;
* Userspace support for the Request API needs to be reviewed;
* Another stateless decoder driver should be submitted;
* At least one stateless encoder driver should be submitted.
* When queueing a request containing references to I frames, the
  refcount of the memory for those I frames needs to be incremented
  and decremented when the request is completed. This will likely
  require some help from vb2. The driver should fail the request
  if the memory/buffer is gone.