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/sifive_fu540_defconfig b/configs/sifive_fu540_defconfig
index 790da97..48eccd7 100644
--- a/configs/sifive_fu540_defconfig
+++ b/configs/sifive_fu540_defconfig
@@ -11,3 +11,4 @@
 CONFIG_DISPLAY_BOARDINFO=y
 CONFIG_OF_PRIOR_STAGE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_DM_MTD=y