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/include/flash.h b/include/flash.h
index 70ab435..807800b 100644
--- a/include/flash.h
+++ b/include/flash.h
@@ -44,7 +44,7 @@
 	uchar   sr_supported;		/* status register supported            */
 	const char *name;		/* human-readable name	                */
 #endif
-#ifdef CONFIG_MTD
+#ifdef CONFIG_DM_MTD
 	struct mtd_info *mtd;
 #endif
 #ifdef CONFIG_CFI_FLASH			/* DM-specific parts */