[PATCH] x86_64: cleanup allocating logical cpu numbers in x86_64

Minor cleanup to lend better for physical CPU hotplug.
Earlier way of using num_processors as index doesnt
fit if CPUs come and go. This makes the code little bit better
to read, and helps physical hotplug use the same functions as boot.

Reserving CPU0 for BSP is too late to be done in smp_prepare_boot_cpu().
Since logical assignments from MADT is already done via
setup_arch()->acpi_boot_init()->parse lapic

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>