Rework the ppc64 hugepage code.  Instead of using specially marked pmd
entries in the normal pagetables to represent hugepages, use normal pte_t
entries, in a special set of pagetables used for hugepages only.

Using pte_t instead of a special hugepte_t makes the code more similar to
that for other architecturess, allowing more possibilities for
consolidating the hugepage code.

Using independent pagetables for the hugepages is also a prerequisite for
moving the hugepages into their own region well outside the normal user
address space.  The restrictions imposed by the powerpc mmu's segment
design mean we probably want to do that in the fairly near future.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>