i2c:pm_smbus: Fix state transfer

Transfer the state information for the SMBus registers and
internal data so it will work on a VM transfer.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

include/hw/i2c/pm_smbus.h

@@ -43,4 +43,13 @@ typedef struct PMSMBus {
 
 void pm_smbus_init(DeviceState *parent, PMSMBus *smb, bool force_aux_blk);
 
+/*
+ * For backwards compatibility on migration, older versions don't have
+ * working migration for pm_smbus, this lets us ignore the migrations
+ * for older machine versions.
+ */
+bool pm_smbus_vmstate_needed(void);
+
+extern const VMStateDescription pmsmb_vmstate;
+
 #endif /* PM_SMBUS_H */