[IA64-SGI] Altix: enable poweroff

This patch adds the necessary "hook" to allow SGI/SN
machines to perform a system power off upon a 
'init 0', 'halt -p', 'poweroff' or 'shutdown -h'.

The "hook" is to set the pm_power_off callback
to ia64_sn_power_down(). pm_power_off is checked
in machine_power_off()/do_poweroff() and, if set, is executed. 
ia64_sn_power_down() is a function already present (but not 
used currently) in the sn kernel.
ia64_sn_power_down() makes a SAL call to execute the
power off.

Signed-off-by: Aaron J Young <ayoung@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/sn/kernel/setup.c

@@ -29,6 +29,7 @@
 #include <linux/sched.h>
 #include <linux/root_dev.h>
 #include <linux/nodemask.h>
+#include <linux/pm.h>
 
 #include <asm/io.h>
 #include <asm/sal.h>
@@ -353,6 +354,14 @@ void __init sn_setup(char **cmdline_p)
 	screen_info = sn_screen_info;
 
 	sn_timer_init();
+
+	/*
+	 * set pm_power_off to a SAL call to allow
+	 * sn machines to power off. The SAL call can be replaced
+	 * by an ACPI interface call when ACPI is fully implemented
+	 * for sn.
+	 */
+	pm_power_off = ia64_sn_power_down;
 }
 
 /**