This is really handy for subsystems that have any attributes they want
to export, esp. if they have just a few, since they don't have to define
all of the infrastructure for creating and tearing down the attributes 
for the high level type that they are. 

- define struct subsys_attribute for declaring attributes of subsystems
themselves. 

- define subsys_create_file() and subsys_remove_file().

- define subsys_sysfs_ops for forwarding sysfs reads and writes to the 
subsystem attribute callbacks. 

- Set the sysfs_ops to be the subsystem ones if the kobject doesn't belong
to a subsystem itself (meaning that it is a subsystem).