s390x: move s390_cpu_addr2state to target/s390x/sigp.c

s390x: move s390_cpu_addr2state to target/s390x/sigp.c

This function has no dependency on the virtio-ccw machine type, though it
assumes that the CPU address corresponds to the core_id and the index.

If there is any need of something different or more fancy (unlikely)
S390 can include a MachineClass subclass and implement it there.  For
now, move it to sigp.c for simplicity.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20240509170044.190795-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>