x86: set cpu_index to nr_cpus instead of 0

Some BIOSes that support two/four dualcore/quadcore systems, will get:

ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled)
Processor #0 15:1 APIC version 16
ACPI: LAPIC (acpi_id[0x02] lapic_id[0x01] enabled)
Processor #1 15:1 APIC version 16
ACPI: LAPIC (acpi_id[0x03] lapic_id[0x02] enabled)
Processor #2 15:1 APIC version 16
ACPI: LAPIC (acpi_id[0x04] lapic_id[0x03] enabled)
Processor #3 15:1 APIC version 16
ACPI: LAPIC (acpi_id[0x05] lapic_id[0x84] disabled)
ACPI: LAPIC (acpi_id[0x06] lapic_id[0x85] disabled)
ACPI: LAPIC (acpi_id[0x07] lapic_id[0x86] disabled)
ACPI: LAPIC (acpi_id[0x08] lapic_id[0x87] disabled)
ACPI: LAPIC (acpi_id[0x09] lapic_id[0x88] disabled)
ACPI: LAPIC (acpi_id[0x0a] lapic_id[0x89] disabled)
ACPI: LAPIC (acpi_id[0x0b] lapic_id[0x8a] disabled)
ACPI: LAPIC (acpi_id[0x0c] lapic_id[0x8b] disabled)
ACPI: LAPIC (acpi_id[0x0d] lapic_id[0x8c] disabled)
ACPI: LAPIC (acpi_id[0x0e] lapic_id[0x8d] disabled)
ACPI: LAPIC (acpi_id[0x0f] lapic_id[0x8e] disabled)
ACPI: LAPIC (acpi_id[0x10] lapic_id[0x8f] disabled)

SMP: Allowing 16 CPUs, 12 hotplug CPUs

the /proc/cpuinfo will show a bunch of NULL cpus with cpu_index=0

so assign impossible cpu_index value at first instead of 0.

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>