mtd: ensure UBI is compiled when using fastmap

UBI must be enabled when using fastmap, reflect this is defconfigs.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/configs/aristainetos_defconfig b/configs/aristainetos_defconfig
index 013a6ba..63d74aa 100644
--- a/configs/aristainetos_defconfig
+++ b/configs/aristainetos_defconfig
@@ -50,6 +50,7 @@
 CONFIG_SF_DEFAULT_SPEED=20000000
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SPI_FLASH_MTD=y
+CONFIG_MTD_UBI=y
 CONFIG_MTD_UBI_FASTMAP=y
 CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT=1
 CONFIG_PHYLIB=y