[IA64] xen_domu_defconfig: fix build issues/warnings

- drivers/xen/events.c did not compile
- xen_setup_hook caused a modpost section warning
- the use of u64 (instead of unsigned long long) together with a %llu
  in drivers/xen/balloon.c caused a compiler warning

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>