spapr: move VCPU calculation to core machine code

spapr: move VCPU calculation to core machine code

The VCPU ids are currently computed and assigned to each individual
CPU threads in spapr_cpu_core_realize(). But the numbering logic
of VCPU ids is actually a machine-level concept, and many places
in hw/ppc/spapr.c also have to compute VCPU ids out of CPU indexes.

The current formula used in spapr_cpu_core_realize() is:

    vcpu_id = (cc->core_id * spapr->vsmt / smp_threads) + i

where:

    cc->core_id is a multiple of smp_threads
    cpu_index = cc->core_id + i
    0 <= i < smp_threads

So we have:

    cpu_index % smp_threads == i
    cc->core_id / smp_threads == cpu_index / smp_threads

hence:

    vcpu_id =
        (cpu_index / smp_threads) * spapr->vsmt + cpu_index % smp_threads;

This formula was used before VSMT at the time VCPU ids where computed
at the target emulation level. It has the advantage of being useable
to derive a VPCU id out of a CPU index only. It is fitted for all the
places where the machine code has to compute a VCPU id.

This patch introduces an accessor to set the VCPU id in a PowerPCCPU object
using the above formula. It is a first step to consolidate all the VCPU id
logic in a single place.

Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>