[IA64] invoke oom-killer from page fault

As explained in commit 1c0fe6e3, we want to call the architecture independent
oom killer when getting an unexplained OOM from handle_mm_fault, rather than
simply killing current.

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>