mtd: ensure MTD is compiled when CMD_MTDPARTS is selected

MTD support must be enabled when using mtdparts. Indeed, functions
like get_mtd_info(), get_mtd_device() and put_mtd_device() are in
drivers/mtd/mtd_uboot.c and are built only with CONFIG_MTD.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/configs/cm_fx6_defconfig b/configs/cm_fx6_defconfig
index 763569d..9f8d71b 100644
--- a/configs/cm_fx6_defconfig
+++ b/configs/cm_fx6_defconfig
@@ -91,3 +91,4 @@
 CONFIG_VIDEO=y
 CONFIG_FDT_FIXUP_PARTITIONS=y
 CONFIG_MTD=y
+CONFIG_MTD_RAW_NAND=y