pseries: Make cpu_update during CAS unconditional

spapr_h_cas_compose_response() includes a cpu_update parameter which
controls whether it includes updated information on the CPUs in the device
tree fragment returned from the ibm,client-architecture-support (CAS) call.

Providing the updated information is essential when CAS has negotiated
compatibility options which require different cpu information to be
presented to the guest.  However, it should be safe to provide in other
cases (it will just override the existing data in the device tree with
identical data).  This simplifies the code by removing the parameter and
always providing the cpu update information.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
