spapr: skip configuration section during migration of older machines

Since QEMU 2.4, we have a configuration section in the migration stream.
This must be skipped for older machines, like it is already done for x86.

This patch fixes the migration of pseries-2.3 from/to QEMU 2.3, but it
breaks migration of the same machine from/to QEMU 2.4/2.4.1/2.5. We do
that anyway because QEMU 2.3 is likely to be more widely deployed than
newer QEMU versions.

Fixes: 61964c2
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
(cherry picked from commit 09b5e30)

Conflicts:
	hw/ppc/spapr.c

*remove dep on 5013c54

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/ppc/spapr.c

@@ -2327,6 +2327,7 @@ static void spapr_compat_2_3(Object *obj)
 {
     savevm_skip_section_footers();
     global_state_set_optional();
+    savevm_skip_configuration();
 }
 
 static void spapr_compat_2_2(Object *obj)