kernel code: example on add sysfs to an kobject

1. Adding to a pre-existing group
   sysfs_add_file_to_group()

2. Adding to a kobject directly
   sysfs_create_file()
kernel_init: some notes on the driver model initialization

Function driver_init() is used to do the initializtion of the driver model.

This function will do the creation of kset of "devices", "dev", "dev/block"
and "dev/char".