apic: fix broken migration for kvm-apic

commit f6e98444 (apic: Use apic_id as apic's migration instance_id)
breaks migration when in kernel irqchip is used for 2.6 and older
machine types.

It applies compat property only for userspace 'apic' type
instead of applying it to all apic types inherited from
'apic-common' type as it was supposed to do.

Fix it by setting compat property 'legacy-instance-id' for
'apic-common' type which affects inherited types (i.e. not
only 'apic' but also 'kvm-apic' types)

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1469800542-11402-1-git-send-email-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/hw/i386/pc.h

@@ -388,7 +388,7 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
         .value = "off",\
     },\
     {\
-        .driver   = "apic",\
+        .driver   = "apic-common",\
         .property = "legacy-instance-id",\
         .value    = "on",\
     },