[OpenBIOS] Fix boot-script parsing for openSUSE ppc media

[laurent at vivier.eu]

>> Fix boot-script parsing for openSUSE ppc media
>
>applied, thanks

I've applied it, as it breaks nothing and allows to use Suse, but a better fix should be:

- correctly parse the script to replace &device; by the boot device ("cd:", and not "cd:0", which is "&bootdevice;:&partition;")

- correctly manage CD partition to be able to use ":1" instead of ":0" (in fact, for the moment, we use mac partition on CD and ":0" to use the entire disk).

Regards,
Laurent