PAPR+ says that no "ibm,purr" tells the guest that H_PURR is not
supported. However some guests still try calling H_PURR on POWER7 unless
the property is present and equal to 0. This adds the property for CPUs
supporting the PURR special register.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Signed-off-by: Alexander Graf <agraf@suse.de>