x86: unify paravirt pagetable accessors

x86: unify paravirt pagetable accessors

Put all the defines for mapping pagetable operations to their native
versions (for the non-paravirt case) into one place.  Make the
corresponding changes to paravirt.h.

The tricky part here is that when a pagetable entry can't be updated
atomically (ie, 32-bit PAE), we need special handlers for pte_clear,
set_pte_atomic and set_pte_present.  However, the other two modes
don't need special handling for these, and can use a common
set_pte(_at) path.

[ mingo@elte.hu: fixes ]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>