[driver model] Add exports for sys devices.

From Dominik Brodowski: 

A few missing exports -- even though the cpu_sysdev_class isn't strictly
needed now, I need it for a few ACPI-related patches I'll send out in a
minute.

drivers/base/cpu.c

@@ -12,6 +12,7 @@
 struct sysdev_class cpu_sysdev_class = {
 	set_kset_name("cpu"),
 };
+EXPORT_SYMBOL(cpu_sysdev_class);
 
 
 /*

drivers/base/sys.c

@@ -158,6 +158,10 @@ void sysdev_driver_unregister(struct sysdev_class * cls,
 	up_write(&system_subsys.rwsem);
 }
 
+EXPORT_SYMBOL(sysdev_driver_register);
+EXPORT_SYMBOL(sysdev_driver_unregister);
+
+
 
 /**
  *	sys_device_register - add a system device to the tree