s390x/kvm: execute "system reset" cpu resets on the vcpu thread

s390x/kvm: execute "system reset" cpu resets on the vcpu thread

Let's execute resets triggered by qemu system resets on the target vcpu thread.
This will avoid synchronize_rcu's in the kernel.

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>