configs: move CONFIG_MTD in defconfigs when set in arch includes

Let's be consistent and always declare CONFIG_MTD from the defconfig
file when needed.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/configs/turris_mox_defconfig b/configs/turris_mox_defconfig
index fafc471..b88cc4b 100644
--- a/configs/turris_mox_defconfig
+++ b/configs/turris_mox_defconfig
@@ -49,6 +49,7 @@
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_SDMA=y
 CONFIG_MMC_SDHCI_XENON=y
+CONFIG_MTD=y
 CONFIG_SF_DEFAULT_MODE=0
 CONFIG_SF_DEFAULT_SPEED=20000000
 CONFIG_SPI_FLASH_MACRONIX=y