[PATCH] x86_64 sync machine_power_off with i386

i386 machine_power_off was disabling the local apic
and all of it's users wanted to be on the boot cpu.
So call machine_shutdown which places us on the boot
cpu and disables the apics.  This keeps us in sync
and reduces the number of cases we need to worry about in
the power management code.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>