s390x/cmma: clean up cmma reset

The cmma reset is per VM, so we don't need a cpu object. We can
directly make use of kvm_state, as it is already available when
the reset is called. By moving the cmma reset in our machine reset
function, we can avoid a manual reset handler.

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>