On qemu_mod_timer_ns, ensure qemu_notify or aio_notify is called to
end the appropriate poll(), irrespective of use_icount value.

On qemu_clock_enable, ensure qemu_notify or aio_notify is called for
all QEMUTimerLists attached to the QEMUClock.
Signed-off-by: NAlex Bligh <alex@alex.org.uk>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>