env: Add !ENV_IS_IN_EXT4 dependency to ENV_IS_NOWHERE

If ENV_IS_IN_EXT4 is set you shouldn't be able to select ENV_IS_NOWHERE.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Petr Vorel <petr.vorel@gmail.com>

env/Kconfig

@@ -3,6 +3,7 @@ menu "Environment"
 config ENV_IS_NOWHERE
 	bool "Environment is not stored"
 	depends on !ENV_IS_IN_EEPROM
+	depends on !ENV_IS_IN_EXT4
 	depends on !ENV_IS_IN_FAT
 	depends on !ENV_IS_IN_FLASH
 	depends on !ENV_IS_IN_MMC