[IA64-SGI] Increase max system size of SGI SN systems

Increase the maximum system size of SGI SN systems. Note that
this is not the maximum SSI size. The maximum system size is
the number of nodes in the numalink domain.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>