Revert "xens_config: disable SCHEDSTATS"

This reverts commit 0553c25f975e98cfdba0d9c1dbb43ace06d434cc.
Revert "xens_config: update"

This reverts commit ce0587d28888be7bcdd2d28ea813a58fef642922.
Revert " sched: Prevent wakeup to enter critical section needlessly"

This reverts commit 753e93cf6f9987e09b04d3faebd607e26e429e70.