in practise, the machines we support don't have
the option of including so many disks; 8 seems like
the most reasonable default. additionally, it's
unreasonable to expect *20 partitions*
this hardcoding is done to avoid using *, which is
slow in grub on some machines (the grub kernel always
re-enumerates the devices during every operation,
without caching any of it)
yet, the hardcoding is also slow; balance it a bit
better by searching fewer permutations, but not so few
that it would likely break a lot of setups
Signed-off-by: Leah Rowe <leah@libreboot.org>