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/mx6sllevk_defconfig b/configs/mx6sllevk_defconfig
index b43648d..4da460d 100644
--- a/configs/mx6sllevk_defconfig
+++ b/configs/mx6sllevk_defconfig
@@ -34,6 +34,7 @@
 CONFIG_DM_I2C=y
 CONFIG_DM_MMC=y
 CONFIG_FSL_USDHC=y
+CONFIG_MTD=y
 CONFIG_PINCTRL=y
 CONFIG_PINCTRL_IMX6=y
 CONFIG_DM_PMIC=y