Add comment and condense code to make use of native_local_ptep_get_and_clear
function.  Also, it turns out the 2-level and 3-level paging definitions were
identical, so move the common definition into pgtable.h
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>