Add scull.c (only assigns major device number)
Add scull.c (only assigns major device number)

Chapter 3 introduces the necessary element to write a fully working
driver. scull.c at this point only assigns a major device number.

Changes to be committed:
	new file:   scull.c

shxdow/practical-reverse-engineering,shxdow/practical-reverse-engineering,shxdow/reverse-engineering,shxdow/practical-reverse-engineering,shxdow/reverse-engineering