Register a sub-device to the asynchronous subdevice framework, and also
create subdevice device node.

Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab+samsung@kernel.org>