Expanded dev_t and char drivers

The type of inode->i_rdev has changed
Is now a straight dev_t
See the new  iminor() and imajor() macros

The old registration interface still works
request_chrdev() allocates minors 0-255 only

New interface gives more flexibility
request_chrdev_region() gets a number range
struct cdev represents a char device
cdev_alloc(), cdev_add(), ... manage those devices
Still subject to change