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/ubi.h b/drivers/mtd/ubi/ubi.h
index c6c2229..d0e3218 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -390,6 +390,8 @@
  * @peb_buf2: another buffer of PEB size used for different purposes
  * @buf_mutex: protects @peb_buf1 and @peb_buf2
  * @ckvol_mutex: serializes static volume checking when opening
+ *
+ * @dbg: debugging information for this UBI device
  */
 struct ubi_device {
 	struct cdev cdev;
@@ -472,6 +474,8 @@
 	void *peb_buf2;
 	struct mutex buf_mutex;
 	struct mutex ckvol_mutex;
+
+	struct ubi_debug_info *dbg;
 };
 
 extern struct kmem_cache *ubi_wl_entry_slab;