V4L/DVB (6342): ivtv: fix circular locking (bug 9037)

If you try to access the video device from within an udev rule,
then you get into a circular locking situation.

Changed the driver to postpone the registration of the devices until
everything else has been fully initialized, so that the newly created
device can be used immediately.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>