parisc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

parisc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by using the yet-unused
_PAGE_ACCESSED location in the swap PTE.  Looking at pte_present() and
pte_none() checks, there seems to be no actual reason why we cannot use
it: we only have to make sure we're not using _PAGE_PRESENT.

Reusing this bit avoids having to steal one bit from the swap offset.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: Helge Deller <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>