xen: arm: handle 40-bit addresses in the p2m

xen: arm: handle 40-bit addresses in the p2m

On the X-gene platform there are resources up this high which must be mapped
to dom0.

Remove the first level page from the p2m->pages list since it is actually two
pages and must be freed as such. Do so in p2m_teardown.

I've also punted on the implementation of dump_p2m_lookup for high
addresses...

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>