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/dra7xx_hs_evm_usb_defconfig b/configs/dra7xx_hs_evm_usb_defconfig
index 6604953..2c4f116 100644
--- a/configs/dra7xx_hs_evm_usb_defconfig
+++ b/configs/dra7xx_hs_evm_usb_defconfig
@@ -81,6 +81,7 @@
 CONFIG_SPL_MMC_HS200_SUPPORT=y
 CONFIG_MMC_OMAP_HS=y
 CONFIG_DM_SPI_FLASH=y
+CONFIG_MTD=y
 CONFIG_SF_DEFAULT_MODE=0
 CONFIG_SF_DEFAULT_SPEED=76800000
 CONFIG_SPI_FLASH_BAR=y