x86: unsigned long pte_pfn

pte_pfn() has always been of type unsigned long, even on 32-bit PAE;
but in the current tip/next/mm tree it works out to be unsigned long
long on 64-bit, which gives an irritating warning if you try to printk
a pfn with the usual %lx.

Now use the same pte_pfn() function, moved from pgtable-3level.h
to pgtable.h, for all models: as suggested by Jeremy Fitzhardinge.
And pte_page() can well move along with it (remaining a macro to
avoid dependence on mm_types.h).

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>