x86/ACPI: keep x86_cpu_to_acpiid mapping valid on CPU hotplug

We may or may not have all possible CPUs in MADT on boot but in any
case we're overwriting x86_cpu_to_acpiid mapping with U32_MAX when
acpi_register_lapic() is called again on the CPU hotplug path:

acpi_processor_hotadd_init()
  -> acpi_map_cpu()
    -> acpi_register_lapic()

As we have the required acpi_id information in acpi_processor_hotadd_init()
propagate it to acpi_map_cpu() to always keep x86_cpu_to_acpiid
mapping valid.

Reported-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>