V4L/DVB (9322): v4l2-int-if: Export more interfaces to modules

Export v4l2_int_device_try_attach_all. This allows initiating the
initialisation of int if device after the drivers have been registered.

Also allow drivers to call ioctls if v4l2-int-if was compiled as
module.

Signed-off-by: Sakari Ailus <sakari.ailus@nokia.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>