The individual gpiod_lookup_table structs cannot be const because they
contain a list-head which gets used when registering them.

But the array of pointers to the gpiod_lookup_table-s used by a board
can be const, constify these.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-By: Lubomir Rintel <lkundrak@V3.sk>
Link: https://lore.kernel.org/r/20220110103952.48760-3-hdegoede@redhat.com