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/j721e_evm_r5_defconfig b/configs/j721e_evm_r5_defconfig
index 62b9594..0b33f04 100644
--- a/configs/j721e_evm_r5_defconfig
+++ b/configs/j721e_evm_r5_defconfig
@@ -71,6 +71,7 @@
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_AM654=y
 CONFIG_DM_SPI_FLASH=y
+CONFIG_MTD=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_PINCTRL=y
 # CONFIG_PINCTRL_GENERIC is not set