pc: acpi: SRAT: create only valid processor lapic entries

When APIC IDs are sparse*, in addition to valid LAPIC
entries the SRAT is also filled invalid ones for non
possible APIC IDs.
Fix it by asking machine for all possible APIC IDs
instead of wrongly assuming that all APIC IDs in
range 0..apic_id_limit are possible.

* sparse lapic topology CLI:
     -smp x,sockets=2,cores=3,maxcpus=6
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>