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/scan.c b/drivers/mtd/ubi/scan.c
index 2135a53..a3a198f 100644
--- a/drivers/mtd/ubi/scan.c
+++ b/drivers/mtd/ubi/scan.c
@@ -1347,7 +1347,7 @@
 	struct ubi_scan_leb *seb, *last_seb;
 	uint8_t *buf;
 
-	if (!(ubi_chk_flags & UBI_CHK_GEN))
+	if (!ubi->dbg->chk_gen)
 		return 0;
 
 	/*