env: Kconfig: Add missing dependency for ENV_IS_IN_EXT4

ENV_IS_IN_EXT4 also need to enable FS_EXT4 which is not covered in Kconfig.
Kconfig reports this as:
WARNING: unmet direct dependencies detected for EXT4_WRITE
  Depends on [n]: FS_EXT4 [=n]
  Selected by [y]:
  - ENV_IS_IN_EXT4 [=y] && !CHAIN_OF_TRUST [=n]

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

env/Kconfig

@@ -72,6 +72,7 @@ config ENV_IS_IN_FAT
 config ENV_IS_IN_EXT4
 	bool "Environment is in a EXT4 filesystem"
 	depends on !CHAIN_OF_TRUST
+	select FS_EXT4
 	select EXT4_WRITE
 	help
 	  Define this if you want to use the EXT4 file system for the environment.