pc: acpi: create Processor and Notify objects only for valid lapics

do not assume that all lapics in range 0..apic_id_limit
are valid and do not create Processor and Notify objects
for not possible lapics.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
