x86/mm: Reorder locks used by shadow code in anticipation of synchronized p2m lookups

x86/mm: Reorder locks used by shadow code in anticipation of synchronized p2m lookups

Currently, mm-locks.h enforces a strict ordering between locks in the mm
layer lest there be an inversion in the order locks are taken and thus
the risk of deadlock.

Once p2m lookups becoming synchronized, get_gfn* calls take the p2m lock, and a
new set of inversion arises.  Reorder some of the locks in the shadow code so
that even in this case no deadlocks happen.

After this, synchronized p2m lookups are in principle ready to be enabled in
shadow mode.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>