Register system calls.

	HW4, let's roll!

	modified:   arch/x86/include/asm/unistd_32.h
	modified:   arch/x86/kernel/syscall_table_32.S
	modified:   include/linux/syscalls.h
Add ssmem.c file.
	Defined the framework of system calls

	new file:   mm/ssmem.c