[IA64] Altix system controller event handling

The following is an update of the patch I sent yesterday
(3/9/05) incorporating suggestions from Christoph Hellwig and
Andreas Schwab.  It allows Altix and Altix-like systems to
handle environmental events generated by the system controllers,
and should apply on top of Jack Steiner's patch of 3/1/05 ("New
chipset support for SN platform") and Mark Goodwin's patch of
3/8/05 ("Altix SN topology support for new chipsets and pci
topology").

Signed-off-by: Greg Howard <ghoward@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>