mtd: ensure MTD is compiled when there is a SPI NOR flash using MTD

MTD must be enabled when there is a SPI NOR flash using the
SPI_FLASH_MTD config entry.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/configs/sama5d27_som1_ek_mmc_defconfig b/configs/sama5d27_som1_ek_mmc_defconfig
index efddb81..1da0bde 100644
--- a/configs/sama5d27_som1_ek_mmc_defconfig
+++ b/configs/sama5d27_som1_ek_mmc_defconfig
@@ -65,6 +65,7 @@
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_ATMEL=y
 CONFIG_DM_SPI_FLASH=y
+CONFIG_MTD=y
 CONFIG_SF_DEFAULT_SPEED=66000000
 CONFIG_SPI_FLASH_ATMEL=y
 CONFIG_SPI_FLASH_MACRONIX=y