This object specify which sub-slot in the pair of
redundancy to be used as prefer sub-slot.
The value of:
primarySubslot(1) is telling the system use the subslot
referred by c64SubSlotConfigModule1Index
and c64SubSlotConfigSubModule1Index as
preferred sub-slot.
secondarySubslot(2) is to use the sub-slot referred by
c64SubSlotConfigModule2Index and
c64SubSlotConfigSubModule2Index.
The default is primarySubslot(1).
The subslot prefer feature is removed and the object
is deprecated