hw/acpi/ich9: clear smi_en on reset

Otherwise on reboot firmware might think (due to APMC_EN remaining set
from the previous boot) that SMI support is absent.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-trivial@nongnu.org
Signed-off-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/acpi/ich9.c

@@ -221,6 +221,7 @@ static void pm_reset(void *opaque)
     acpi_pm_tmr_reset(&pm->acpi_regs);
     acpi_gpe_reset(&pm->acpi_regs);
 
+    pm->smi_en = 0;
     if (!pm->smm_enabled) {
         /* Mark SMM as already inited to prevent SMM from running. KVM does not
          * support SMM mode. */