mtd: rename CONFIG_MTD -> CONFIG_DM_MTD

CONFIG_MTD must be reserved for the MTD core. Like any other
subsystem, prefix the symbol by DM when it comes to DM support.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
[trini: Add Kconfig files]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/dfu/Kconfig b/drivers/dfu/Kconfig
index 9fe5bc0..02bc28f 100644
--- a/drivers/dfu/Kconfig
+++ b/drivers/dfu/Kconfig
@@ -56,7 +56,7 @@
 
 config DFU_MTD
 	bool "MTD back end for DFU"
-	depends on MTD
+	depends on DM_MTD
 	help
 	  This option enables using DFU to read and write to on any MTD device.