s390x: machine reset function with new ipl cpu handling

Current implementation depends on the order of resets getting triggered.

If a cpu reset is triggered after the ipl device reset, the CPU is stopped and
the VM will not run. In fact, that hinders us from converting the ipl device
into a TYPE_DEVICE. Let's change that by manually configuring the ipl cpu
during a system reset, so we have full control and can demangle that code.

Also remove the superflous cpu parameter from s390_update_iplstate on the way.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>