sysfs: Document sysfs_attr_init and sysfs_bin_attr_init

I have added a new requirement to the external sysfs interface
that dynamically allocated sysfs attributes must call sysfs_attr_init
if lockdep is enabled.  For the time being callying sysfs_attr_init
is only mandatory if lockdep is enabled, so we can live with a few
unconverted instances until we find them all.  As this is part of
the public interface of sysfs it is a good idea to document these
pseudo functions so someone inspeciting the code can find out
what has happened.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>