mtd: rename CONFIG_MTD_DEVICE -> CONFIG_MTD

Like in Linux, just use CONFIG_MTD to compile the MTD stack.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/configs/variscite_dart6ul_defconfig b/configs/variscite_dart6ul_defconfig
index 7178b8e..9387c3b 100644
--- a/configs/variscite_dart6ul_defconfig
+++ b/configs/variscite_dart6ul_defconfig
@@ -35,6 +35,7 @@
 CONFIG_DM_I2C_GPIO=y
 CONFIG_SYS_I2C_MXC=y
 CONFIG_FSL_USDHC=y
+CONFIG_MTD=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_MICREL=y
 CONFIG_FEC_MXC=y