s390: fix cpu hotplug / cpu activity on interrupts

The add_del/running_cpu code and env->halted are tracking stopped cpus.
Sleeping cpus (idle and enabled for interrupts) are waiting inside the
kernel.
No interrupt besides the restart can move a cpu from stopped to
operational. This is already handled over there. So lets just remove
the bogus wakup from the common interrupt delivery, otherwise any
interrupt will wake up a cpu, even if this cpu is stopped (Thus leading
to strange hangs on sigp restart)

This fixes
echo 0 > /sys/devices/system/cpu/cpu0/online
echo 1 > /sys/devices/system/cpu/cpu0/online
in the guest

Signed-off-by: Christian <Borntraeger&lt;borntraeger@de.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>