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/sata.c

@@ -111,7 +111,7 @@ static void env_sata_load(void)
 		return -EIO;
 	}
 
-	return env_import(buf, 1);
+	return env_import(buf, 1, H_EXTERNAL);
 }
 
 U_BOOT_ENV_LOCATION(sata) = {