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/configs/10m50_defconfig b/configs/10m50_defconfig
index 138bb52..e99e975 100644
--- a/configs/10m50_defconfig
+++ b/configs/10m50_defconfig
@@ -26,7 +26,7 @@
 CONFIG_ALTERA_PIO=y
 CONFIG_MISC=y
 CONFIG_ALTERA_SYSID=y
-CONFIG_MTD=y
+CONFIG_DM_MTD=y
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_MTD_DEVICE=y
 CONFIG_ALTERA_QSPI=y