efi_loader: Ignore DT when ACPI is on

For targets that enable ACPI, we should not pass Device Trees into
the payload. However, our distro boot logic always passes the builtin
DT as an argument.

To make it easy to use ACPI with distro boot, let's just ignore the DT
argument to bootefi when ACPI is enabled. That way, we can successfully
distro boot payloads on ACPI enabled targets.

Signed-off-by: Alexander Graf <agraf@csgraf.de>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>