Add support for allocating root device objects which group
device objects under /sys/devices directories.

Also add a sysfs 'module' symlink which points to the owner
of the root device object. This symlink will be used in virtio
to allow userspace to determine which virtio bus implementation
a given device is associated with.

[Includes suggestions from Cornelia Huck]
Signed-off-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>