ia64/xen: a recipe for using xen/ia64 with pv_ops.

Recipe for using xen/ia64 with pv_ops domU.

Signed-off-by: Akio Takebe <takebe_akio@jp.fujitsu.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>