dm: core: Don't show an ACPI warning if there is no ordering

Some boards don't care about the ordering of ACPI code fragments. Change
the warning to a debug message.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>