ARM: convert to generated system call tables

Convert ARM to use a similar mechanism to x86 to generate the unistd.h
system call numbers and the various kernel system call tables.  This
means that rather than having to edit three places (asm/unistd.h for
the total number of system calls, uapi/asm/unistd.h for the system call
numbers, and arch/arm/kernel/calls.S for the call table) we have only
one place to edit, making the process much more simple.

The scripts have knowledge of the table padding requirements, so there's
no need to worry about __NR_syscalls not fitting within the immediate
constant field of ALU instructions anymore.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>