bcache: Debug code improvements

Couple changes:
 * Consolidate bch_check_keys() and bch_check_key_order(), and move the
   checks that only check_key_order() could do to bch_btree_iter_next().

 * Get rid of CONFIG_BCACHE_EDEBUG - now, all that code is compiled in
   when CONFIG_BCACHE_DEBUG is enabled, and there's now a sysfs file to
   flip on the EDEBUG checks at runtime.

 * Dropped an old not terribly useful check in rw_unlock(), and
   refactored/improved a some of the other debug code.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/btree.h

@@ -259,14 +259,6 @@ static inline void rw_lock(bool w, struct btree *b, int level)
 
 static inline void rw_unlock(bool w, struct btree *b)
 {
-#ifdef CONFIG_BCACHE_EDEBUG
-	unsigned i;
-
-	if (w && b->key.ptr[0])
-		for (i = 0; i <= b->nsets; i++)
-			bch_check_key_order(b, b->sets[i].data);
-#endif
-
 	if (w)
 		b->seq++;
 	(w ? up_write : up_read)(&b->lock);