Add _addr_lsb field to ia64 siginfo

The huge pages code uses the siginfo _addr_lsb field, but ia64
was missing it. Add it to ia64 too (over some padding) to avoid
compilation failures.

Acked-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>