cmd: ubi: add a command to rename volume

This commit adds the command ubi rename to rename an ubi volume.
The format of the command is: ubi rename <oldname> <newname>.
To enable this command, the option CMD_UBI_RENAME must be selected.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index faa133d..1c9634d 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -2173,6 +2173,14 @@
 	  It is also strongly encouraged to also enable CONFIG_MTD to get full
 	  partition support.
 
+config CMD_UBI_RENAME
+       bool "Enable rename"
+       depends on CMD_UBI
+       default n
+       help
+         Enable a "ubi" command to rename ubi volume:
+	   ubi rename <oldname> <newname>
+
 config CMD_UBIFS
 	tristate "Enable UBIFS - Unsorted block images filesystem commands"
 	depends on CMD_UBI