spapr: Don't allow multiple active vCPUs at CAS

spapr: Don't allow multiple active vCPUs at CAS

According to the description of "ibm,client-architecture-support" that
can found in LoPAPR "B.6.2.3 Root Node Methods":

If multiple partition processors or threads are active at the time of
the ibm,client-architecture-support method call, or an error is detected
in the format of the ibm,architecture.vec structure, the err? boolean
shall be TRUE; else FALSE.

We certainly don't want to temper with the platform or with the PCR of
the other vCPUs if they happen to be active. Ensure we have only one
active vCPU and fail CAS otherwise. This is just for conformance and
robustness, it doesn't fix any known bugs.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <157969867170.571404.12117797348882189656.stgit@bahia.lan>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>