bugfix: vm halt when in reset looping

reset mc146818rtc device when RESET event happens.

Fix the problem:
  1. Guest boot the second cpu, set CMOS_RESET_CODE 0x0a to protect selfboot;
  2. VM being reset by others, hmp_system_reset;
  3. seabios resume check the CMOS_RESET_CODE, if 0x0a, jump to the BDA
     resume execution by jump via 40h:0067h;
  4. Guest halt;
Signed-off-by: Nhangaohuai <hangaohuai@huawei.com>
Message-Id: <20161219060336.10176-1-hangaohuai@huawei.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/timer/mc146818rtc.c

@@ -946,11 +946,23 @@ static Property mc146818rtc_properties[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
+static void rtc_resetdev(DeviceState *d)
+{
+    RTCState *s = MC146818_RTC(d);
+
+    /* Reason: VM do suspend self will set 0xfe
+     * Reset any values other than 0xfe(Guest suspend case) */
+    if (s->cmos_data[0x0f] != 0xfe) {
+        s->cmos_data[0x0f] = 0x00;
+    }
+}
+
 static void rtc_class_initfn(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
 
     dc->realize = rtc_realizefn;
+    dc->reset = rtc_resetdev;
     dc->vmsd = &vmstate_rtc;
     dc->props = mc146818rtc_properties;
     /* Reason: needs to be wired up by rtc_init() */