s390x/kvm: execute the first cpu reset on the vcpu thread

s390x/kvm: execute the first cpu reset on the vcpu thread

As all full cpu resets currently call into the kernel to do initial cpu reset,
let's run this reset (triggered by cpu_s390x_init()) on the proper vcpu thread.

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