spapr: Restore support for older PowerPC CPU cores

Introduction of core based CPU hotplug for PowerPC sPAPR didn't
add support for 970 and POWER5+ based core types. Add support for
the same.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>