mtd: ensure UBI is compiled when ENV_IS_IN_UBI is selected

UBI must be enabled when the environment is in UBI.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/env/Kconfig b/env/Kconfig
index bc88c59..ed12609 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -366,6 +366,8 @@
 config ENV_IS_IN_UBI
 	bool "Environment in a UBI volume"
 	depends on !CHAIN_OF_TRUST
+	depends on MTD_UBI
+	depends on CMD_UBI
 	help
 	  Define this if you have an UBI volume that you want to use for the
 	  environment.  This has the benefit of wear-leveling the environment