[AFS]: Eliminate cmpxchg() usage in vlocation code.

cmpxchg() is not available on every processor so can't
be used in generic code.

Replace with spinlock protection on the ->state changes,
wakeups, and wait loops.

Add what appears to be a missing wakeup on transition
to AFS_VL_VALID state in afs_vlocation_updater().

Signed-off-by: David S. Miller <davem@davemloft.net>

fs/afs/internal.h

@@ -219,7 +219,7 @@ struct afs_vlocation {
 	struct afs_volume	*vols[3];	/* volume access record pointer (index by type) */
 	wait_queue_head_t	waitq;		/* status change waitqueue */
 	time_t			update_at;	/* time at which record should be updated */
-	rwlock_t		lock;		/* access lock */
+	spinlock_t		lock;		/* access lock */
 	afs_vlocation_state_t	state;		/* volume location state */
 	unsigned short		upd_rej_cnt;	/* ENOMEDIUM count during update */
 	unsigned short		upd_busy_cnt;	/* EBUSY count during update */