When falcon mode is enabled and SPL_OS_BOOT_SECURE is not enabled,
restore the previous default behavior of having an args file be
expected. Platforms which are using a FIT image here and do not need
this can update at their convenience to disable this option now.
Fixes: b1a3ed0688 ("spl: make args file optional in falcon mode")
Signed-off-by: Tom Rini <trini@konsulko.com>