Implement pte_numa and pmd_numa.

We must atomically set the numa bit and clear the present bit to
define a pte_numa or pmd_numa.

Once a pte or pmd has been set as pte_numa or pmd_numa, the next time
a thread touches a virtual address in the corresponding virtual range,
a NUMA hinting page fault will trigger. The NUMA hinting page fault
will clear the NUMA bit and set the present bit again to resolve the
page fault.

The expectation is that a NUMA hinting page fault is used as part
of a placement policy that decides if a page should remain on the
current node or migrated to a different node.
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NMel Gorman <mgorman@suse.de>