[media] siano: add support for the media controller at USB driver

Adding support for the media controller for a pure DVB device
is simple: just create a struct media_device and add it to the
dvb adapter. After creating all DVB devices, we need to call
the DVB core, for it to create the media graph.

More work is needed for pure DVB tuners, but this is hidden
at the Siano driver, just like several others non-hybrid
devices. So, this is streight forward.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>