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: hangaohuai <hangaohuai@huawei.com>
Message-Id: <20161219060336.10176-1-hangaohuai@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
