s390x: kvm: Fix number of cpu reports for stsi 3.2.2

The cpu number reporting is handled by KVM and QEMU only fills in the
VM name, uuid and other values.

Unfortunately KVM doesn't report reserved cpus and doesn't even know
they exist until the are created via the ioctl.

So let's fix up the cpu values after KVM has written its values to the
3.2.2 sysib. To be consistent, we use the same code to retrieve the cpu
numbers as the STSI TCG code in target/s390x/misc_helper.c:HELPER(stsi).

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200331110123.3774-1-frankja@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>