Convert CONFIG_MTD_CONCAT to Kconfig

This converts the following to Kconfig:
  CONFIG_MTD_CONCAT

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
index 588ebe9..4088267 100644
--- a/drivers/mtd/Kconfig
+++ b/drivers/mtd/Kconfig
@@ -22,6 +22,14 @@
 	help
 	  Enable support for parallel NOR flash.
 
+config MTD_CONCAT
+	bool "Enable MTD device concatenation"
+	depends on MTD
+	help
+	  Enable support for concatenating multiple physical MTD devices
+	  into a single logical device. The larger logical device can then
+	  be partitioned.
+
 config SYS_MTDPARTS_RUNTIME
 	bool "Allow MTDPARTS to be configured at runtime"
 	depends on MTD