ia64/xen: introduce sync bitops which is necessary for ia64/xen support.

define sync bitops which is necessary for ia64/xen.
This bit operation is used to communicate with VMM or other guest kernel
Even when this kernel is built for UP, VMM might be SMP so that those operation
must always use atomic operation.

Cc: Robin Holt <holt@sgi.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Tony Luck <tony.luck@intel.com>