UBI: use debugfs for the extra checks knobs

This patch introduces debugfs support to UBI. All the UBI stuff is kept in the
"ubi" debugfs directory, which contains per-UBI device "ubi/ubiX"
sub-directories, containing debugging files. This file also creates
"ubi/ubiX/chk_gen" and "ubi/ubiX/chk_io" knobs for switching general and I/O
extra checks on and off. And it removes the 'debug_chks' UBI module parameters.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/vtbl.c b/drivers/mtd/ubi/vtbl.c
index fd3bf77..d704ad2 100644
--- a/drivers/mtd/ubi/vtbl.c
+++ b/drivers/mtd/ubi/vtbl.c
@@ -876,7 +876,7 @@
  */
 static void paranoid_vtbl_check(const struct ubi_device *ubi)
 {
-	if (!(ubi_chk_flags & UBI_CHK_GEN))
+	if (!ubi->dbg->chk_gen)
 		return;
 
 	if (vtbl_check(ubi, ubi->vtbl)) {