Relax placement of immobile subspaces
Remove restriction that varyobj subspace be higher in memory and that they abut.
The intent is to allow loading at least the code as an ELF section.
The major change is to treat the two as completely separate from an addressing
standpoint. Page indices start from 0 in each subspace rather than having one
pick up where the other left off. find_immobile_page_index() ceases to exist.
Its replacements are find_varyobj_page_index() and find_fixedobj_page_index().
Similarly varyobj_page_address() and fixedobj_page_address().