More mddev tidyup - remove recovery_sem and resync_sem

recovery_sem and resync_sem get replaced by careful use
of recovery_running protected by reconfig_sem.

As part of this, the creative:
	down(&mddev->recovery_sem);
	up(&mddev->recovery_sem);

when stopping an array gets replaced by a more obvious

	wait_event(resync_wait, mddev->recovery_running <= 0);