A number of random changes to make xen/smp.c compile in 64-bit mode.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>a
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>