env: Discern environment coming from external storage

Add another custom environment flag which discerns environment coming
from external storage from environment set by U-Boot itself.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>

env/fat.c

@@ -144,7 +144,7 @@ static int env_fat_load(void)
 		goto err_env_relocate;
 	}
 
-	return env_import(buf, 1);
+	return env_import(buf, 1, H_EXTERNAL);
 
 err_env_relocate:
 	env_set_default(NULL, 0);