mtd: mtdcore: add debugfs nodes for querying the flash name and id

Currently, we don't have vfs nodes for querying the underlying flash name
and flash id. This information is important especially when we want to
know the flash detail of the defective system. In order to support the
query, we add mtd_debugfs_populate() to create two debugfs nodes
(ie. partname and partid). The upper driver can assign the pointer to
partname and partid before calling mtd_device_register().

Signed-off-by: Zhuohao Lee <zhuohao@chromium.org>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>

include/linux/mtd/mtd.h

@@ -189,6 +189,9 @@ struct module;	/* only needed for owner field in mtd_info */
  */
 struct mtd_debug_info {
 	struct dentry *dfs_dir;
+
+	const char *partname;
+	const char *partid;
 };
 
 struct mtd_info {