cpus: define QEMUTimerListNotifyCB for QEMU system emulation

There is no change for now, because the callback just invokes
qemu_notify_event.

Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tests/test-aio-multithread.c

@@ -438,7 +438,7 @@ static void test_multi_mutex_10(void)
 
 int main(int argc, char **argv)
 {
-    init_clocks();
+    init_clocks(NULL);
 
     g_test_init(&argc, &argv, NULL);
     g_test_add_func("/aio/multi/lifecycle", test_lifecycle);