[mmotm] pm: fix build error

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

Hi

My IA64 machine can't build on today's mmotm(Jul 13).
So, below patch is necessary, I think.

----------------------------------------------------
Against: mmotm, Jul 13
Applies after: pm-schedule-sysrq-poweroff-on-boot-cpu.patch

Now, handle_poweroff() use cpu_online_map variable.
So cpumask.h sould be included.
Otherwise it cause following build error on ia64 (I guess also sevaral othor platfom).

	kernel/power/poweroff.c: In function 'handle_poweroff':
	kernel/power/poweroff.c:29: error: implicit declaration of function 'first_cpu'
	kernel/power/poweroff.c:29: error: 'cpu_online_map' undeclared (first use in this function)
	kernel/power/poweroff.c:29: error: (Each undeclared identifier is reported only once
	kernel/power/poweroff.c:29: error: for each function it appears in.)
	make[2]: *** [kernel/power/poweroff.o] Error 1
	make[1]: *** [kernel/power] Error 2


Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Zhang Rui <rui.zhang@intel.com>
CC: Rus <harbour@sfinx.od.ua>
CC: Rafael J. Wysocki <rjw@sisk.pl>
CC: Pavel Machek <pavel@ucw.cz>

---
 kernel/power/poweroff.c |    1 +
 1 file changed, 1 insertion(+)

Index: b/kernel/power/poweroff.c
===================================================================
--- a/kernel/power/poweroff.c
+++ b/kernel/power/poweroff.c
@@ -10,6 +10,7 @@
 #include <linux/pm.h>
 #include <linux/workqueue.h>
 #include <linux/reboot.h>
+#include <linux/cpumask.h>
 
 /*
  * When the user hits Sys-Rq o to power down the machine this is the