UBI: make tests modes dynamic

Similarly to the debugging checks and message, make the test modes
be dynamically selected via the "debug_tsts" module parameter or
via the "/sys/module/ubi/parameters/debug_tsts" sysfs file. This
is consistent with UBIFS as well.

And now, since all the Kconfig knobs became dynamic, we can remove
the Kconfig.debug file completely.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 4e55290..b4cf57d 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -613,7 +613,7 @@
 	list_add_tail(&wrk->list, &ubi->works);
 	ubi_assert(ubi->works_count >= 0);
 	ubi->works_count += 1;
-	if (ubi->thread_enabled)
+	if (ubi->thread_enabled && !ubi_dbg_is_bgt_disabled())
 		wake_up_process(ubi->bgt_thread);
 	spin_unlock(&ubi->wl_lock);
 }
@@ -1364,7 +1364,7 @@
 
 		spin_lock(&ubi->wl_lock);
 		if (list_empty(&ubi->works) || ubi->ro_mode ||
-			       !ubi->thread_enabled) {
+		    !ubi->thread_enabled || ubi_dbg_is_bgt_disabled()) {
 			set_current_state(TASK_INTERRUPTIBLE);
 			spin_unlock(&ubi->wl_lock);
 			schedule();