hw/acpi/ich9_tco: Include missing 'migration/vmstate.h' header

We need the VMStateDescription structure definition from
"migration/vmstate.h" in order to declare vmstate_tco_io_sts.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Message-Id: <20240219141412.71418-4-philmd@linaro.org>

include/hw/acpi/ich9_tco.h

@@ -11,6 +11,7 @@
 #define HW_ACPI_TCO_H
 
 #include "exec/memory.h"
+#include "migration/vmstate.h"
 
 /* As per ICH9 spec, the internal timer has an error of ~0.6s on every tick */
 #define TCO_TICK_NSEC 600000000LL