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/smdk5420_defconfig b/configs/smdk5420_defconfig
index 968f3a1..ec35a91 100644
--- a/configs/smdk5420_defconfig
+++ b/configs/smdk5420_defconfig
@@ -36,6 +36,7 @@
 CONFIG_MMC_DW=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_S5P=y
+CONFIG_MTD=y
 CONFIG_SF_DEFAULT_MODE=0
 CONFIG_SF_DEFAULT_SPEED=50000000
 CONFIG_SPI_FLASH_GIGADEVICE=y