pit: fix pit interrupt can't inject into vm after migration

kvm_pit is running in kmod. kvm_pit is going to inject
interrupt to vm before cpu_synchronize_all_post_init at
dest side. vcpu will lose the pit interrupt, but
ack_irq(in kmod) has been 0. ack_irq become 1 after
vcpu responds pit interrupt. pit interruptcan inject
to vm when ack_irq is 1.

By the way, kvm_pit_vm_state_change has save and load
state of pit, so pre_save and post_load is unnecessary.

Signed-off-by: ChenLiang <chenliang88@huawei.com>
Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/kvm/i8254.c

@@ -239,6 +239,7 @@ static void kvm_pit_vm_state_change(void *opaque, int running,
 
     if (running) {
         kvm_pit_update_clock_offset(s);
+        kvm_pit_put(PIT_COMMON(s));
         s->vm_stopped = false;
     } else {
         kvm_pit_update_clock_offset(s);
@@ -314,8 +315,6 @@ static void kvm_pit_class_init(ObjectClass *klass, void *data)
     dc->realize = kvm_pit_realizefn;
     k->set_channel_gate = kvm_pit_set_gate;
     k->get_channel_info = kvm_pit_get_channel_info;
-    k->pre_save = kvm_pit_get;
-    k->post_load = kvm_pit_put;
     dc->reset = kvm_pit_reset;
     dc->props = kvm_pit_properties;
 }